network attached storage
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05-01-2010, 05:15 PM



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ABSTRACT
The incremental growth of the Internet for communications within and between companies has raised an important issue of where and how to store all the information being generated and to ensure it is safe and secure in the event of system crashes and other crises. As a result the need for an optimized storage solution becomes essential. Network Attached Storage (NAS) is becoming a critical technology in this environment. The benefit of NAS over the older technologies is that it separates servers and storage, resulting in reduced costs and easier implementation. As the name implies, NAS attaches directly to the LAN, providing direct access to the file system and disk storage. Unlike older technologies, the application layer no longer resides on the NAS platform, but on the client itself. This frees the NAS processor from functions that would ultimately slow down its ability to provide fast responses to data requests.

INTRODUCTION
Information Technology (IT) departments are looking for cost-effective storage solutions that can offer performance, scalability, and reliability. As users on the network increase and the amounts of data generated multiply, the need for an optimized storage solution becomes essential. Network Attached Storage (NAS) is becoming a critical technology in this environment.
The benefit of NAS over the older Direct Attached Storage (DAS) technology is that it separates servers and storage, resulting in reduced costs and easier implementation. As the name implies, NAS attaches directly to the LAN, providing direct access to the file system and disk storage. Unlike DAS, the application layer no longer resides on the NAS platform, but on the client itself. This frees the NAS processor from functions that would ultimately slow down its ability to provide fast responses to data requests.
In addition, this architecture gives NAS the ability to service both Network File System (NFS) and Common Internet File System (CIFS) clients. As shown in the figure below, this allows the IT manager to provide a single shared storage solution that can simultaneously support both Windows*-and UNIX*-based clients and servers. In fact, a NAS system equipped with the right file system software can support clients based on any operating system.
NAS is typically implemented as a network appliance, requiring a small form factor (both real estate and height) as well as ease of use. NAS is a solution that meets the ever-demanding needs of today's networked storage market.

NAS Appliance in a Local Area Network

NETWORK STORAGE CONCEPTS
In basic terms, network storage is simply about storing data using a method by which it can be made available to clients on the network. Over the years, the storage of data has evolved through various phases. This evolution has been driven partly by the changing ways in which we use technology, and in part by the exponential increase in the volume of data we need to store. It has also been driven by new technologies, which allow us to store and manage data in a more effective manner.
In the days of mainframes, data was stored physically separate from the actual processing unit, but was still only accessible through the processing units. As PC based servers became more commonplace, storage devices went 'inside the box' or in external boxes that were connected directly to the system. Each of these approaches was valid in its time, but as our need to store increasing volumes of data and our need to make it more accessible grew, other alternatives were needed. Enter network storage.
Network storage is a generic term used to describe network based data storage, but there are many technologies within it which all go to make the magic happen. Here is a rundown of some of the basic terminology that you might happen across when reading about network storage.
Direct Attached Storage (DAS)
Direct attached storage is the term used to describe a storage device that is directly attached to a host system. The simplest example of DAS is the internal hard drive of a server computer, though storage devices housed in an external box come under this banner as well. DAS is still, by far, the most common method of storing data for computer systems. Over the years, though, new technologies have emerged which work, if you'll excuse the pun, out of the box.
Network Attached Storage (NAS)
Network Attached Storage, or NAS, is a data storage mechanism that uses special devices connected directly to the network media. These devices are assigned an IP address and can then be accessed by clients via a server that acts as a gateway to the data, or in some cases allows the device to be accessed directly by the clients without an intermediary.
The beauty of the NAS structure is that it means that in an environment with many servers running different operating systems, storage of data can be centralized, as can the security, management, and backup of the data. An increasing number of companies already make use of NAS technology, if only with devices such as CD-ROM towers (stand-alone boxes that contain multiple CD-ROM drives) that are connected directly to the network.
Some of the big advantages of NAS include the expandability; need more storage space, add another NAS device and expand the available storage. NAS also bring an extra level of fault tolerance to the network. In a DAS environment, a server going down means that the data that that server holds is no longer available. With NAS, the data is still available on the network and accessible by clients. Fault tolerant measures such as RAID, can be used to make sure that the NAS device does not become a point of failure.

Storage Area Network (SAN)
A SAN is a network of storage devices that are connected to each other and to a server, or cluster of servers, which act as an access point to the SAN. In some configurations a SAN is also connected to the network. SAN's use special switches as a mechanism to connect the devices. These switches, which look a lot like a normal Ethernet networking switch, act as the connectivity point for SAN's. Making it possible for devices to communicate with each other on a separate network brings with it many advantages. Consider, for instance, the ability to back up every piece of data on your network without having to 'pollute' the standard network infrastructure with gigabytes of data. This is just one of the advantages of a SAN which is making it a popular choice with companies today, and is a reason why it is forecast to become the data storage technology of choice in the coming years.

WHAT IS NETWORK ATTACHED STORAGE
Network-attached storage (NAS) is hard disk storage that is set up with its own network address rather than being attached to the department computer that is serving applications to a network's workstation users. By removing storage access and its management from the department server, both application programming and files can be served faster because they are not competing for the same processor resources. The network-attached storage device is attached to a local area network (typically, an Ethernet network) and assigned an IP address. File requests are mapped by the main server to the NAS file server.
A network-attached storage (NAS) device is a server that is dedicated to nothing more than file sharing. NAS does not provide any of the activities that a server in a server-centric system typically provides, such as e-mail, authentication or file management. NAS allows more hard disk storage space to be added to a network that already utilizes servers without shutting them down for maintenance and upgrades. With a NAS device, storage is not an integral part of the server. Instead, in this storage-centric design, the server still handles all of the processing of data but a NAS device delivers the data to the user. A NAS device does not need to be located within the server but can exist anywhere in a LAN and can be made up of multiple networked NAS devices.
Network Attached Storage separates the application server from the storage. This increases overall system performance by allowing the servers to perform application requests and the NAS to serve files or run applications.

NAS BLOCK DIAGRAM


FUNCTIONAL DESCRIPTION
Midrange NAS Architecture
The proposed platform in this section is a midrange NAS appliance. This type of platform is typically housed in a 1U rack and scales to several terabytes of storage across eight or more SCSI drives controlled by hardware-based RAID. Dual processors, fast PCI-X I/O, and fast DDR memory all contribute to system performance while redundant Gigabit Ethernet connections help reduce LAN bottlenecks.
Intel Pentium III processor with 512 KB L2 Cache: The Intel Pentium III processor with 512 KB L2 Cache is an excellent solution for NAS appliances. The Pentium III processor implements a Dynamic Execution micro architecture”a unique combination of multiple branch prediction, data flow analysis, and speculative execution. This enables the Pentium III processor to deliver higher performance while maintaining binary compatibility with all previous Intel Architecture processors. The processor also executes Intel® MMX„¢ technology instructions for enhanced media and communication performance. Additionally, the Pentium III processor executes Streaming Single-Instruction Multiple Data (SIMD) Extensions for enhanced floating-point performance. Data prefetch logic adds functionality that anticipates the data needed by the application and pre-loads it into the advanced transfer cache. The processor utilizes multiple low-power states to conserve power during idle times. The Pentium III processor is available in either a 478-pin FCPGA2 or a 479-ball micro FCBGA, and supports core frequencies ranging from 800 MHz to 1.26 GHz.
IOP321 I/O Processor: The IOP321 is a single function device that integrates a 600 MHz Intel® XScale„¢ core with intelligent peripherals including a PCI bus, which supports 133 MHz operation in PCI-X mode. Other integrated features include an address translation unit, messaging unit, DMA, peripheral bus interface unit, memory controller for PC200 DDR SDRAM, application accelerator unit, and I2C interface. The I/O processor offloads the RAID function from the host processor resulting in increased performance.
82546EB Dual Port Gigabit Ethernet Controller: The 82546EB integrates a dual 10/100/1000 Mbps MAC and PHY into a single 21 x 21 mm BGA package. The device is optimized for enterprise networking and server appliances that use PCI or PCI-X.
Processor System Bus (PSB): The Pentium III processor uses the original low voltage signaling of the Gunning Transceiver Logic (GTL) technology for the system bus. The GTL system bus operates at 1.25V signal levels vs. GTL+, which operates at 1.5V signal levels. This bus provides a 32-bit address bus with a 64-bit data bus at 133 MHz, resulting in a total bandwidth of 1 GB/s.
Double Data Rate (DDR) Memory Bus: The integrated memory controller provides a single 64-bit wide (72-bit for ECC) DDR memory channel supporting up to 8 GB of local memory. The address and control bus operates at 100 or 133 MHz. Data is acquired on the rising and falling edge of the clock doubling the data rate to 200 or 266 MHz, providing bandwidths of 1.6 GB/s and 2.1 GB/s respectively.
Peripheral Component Interconnect eXtended (PCI-X): PCI-X enables the design of systems and devices that operate at clock speeds up to 133 MHz, or 1 GB/s. The PCI-X protocol enhancements enable devices to operate much more efficiently, thereby providing more usable bandwidth at any clock frequency. PCI-X provides backward compatibility by allowing devices to operate at conventional PCI frequencies and modes when installed in conventional systems. The PCI-X bus provides a 64-bit data bus that is capable of running at 133 MHz with one device providing 1 GB/s bandwidth, 100 MHz with two devices providing 800 MB/s bandwidth, and 66 MHz with three or four devices providing 533 MB/s bandwidth.
Peripheral Component Interconnect (PCI): The PCI local bus is a high-performance 64-bit bus with multiplexed address and data lines, all running at 33 MHz, providing a total bandwidth of 266 MB/s.
ATA100: The ATA100 logic can achieve read transfer rates up to 100 MB/s and write transfer rates up to 88.9 MB/s and is backwards compatible with ATA66, ATA33 and PIO modes. The cable improvements required for ATA66 are sufficient for ATA100, so no further cable improvements are required when implementing ATA100. Different timings can be programmed for each drive in the system, allowing drives of different types to run at full speed on the same cable.
Small Computer Systems Interface (SCSI): SCSI is the traditional storage channel technology for open system servers. It allows overlapped operations, which means that SCSI Host Bus Adapters (HBAs) can multitask their operations. It supports data intensive applications and a wide variety of devices. SCSI generally spans the midrange product segment.
S-ATA: Serial ATA is another option for high-speed disk connectivity. It offers faster performance than parallel ATA and it is approaching SCSI. It offers thinner cabling, lower power, and lower pin count interfaces vs. ATA or SCSI. S-ATA technology will deliver 150 MB/s of performance to each drive within a disk drive array, and the roadmap specifies 300 MB/s and 600 MB/s throughputs to support generations of storage evolution. The various products and interfaces described above ensure high performance in the proposed NAS appliance design.
NAS Appliance Theory of Operation
A NAS device is essentially a plug-and-play storage appliance, designed to respond to client requests for stored data in real time. NAS devices are well suited to serve networks that have a heterogeneous mix of clients and servers, such as UNIX*, Microsoft Windows*, and Linux*. The NAS appliance can do this by running a suite of file system software compatible with the clients it services. When a client on the LAN requests data from the storage system, the application layer of the client sends a data request over the network to the NAS platform. The local file system of the NAS determines the origin of the request and sends the appropriately formatted data back to the originating client.
A NAS system provides file security, through methods such as Access Control Lists, and it performs all file and storage services through standard network protocols, including TCP/IP for data transfer, Ethernet for media access, and HTTP, CIFS, and NFS for remote file services. In addition, a high-performance NAS appliance may handle tasks such as Web cache and proxy, audio and video streaming, and tape backup.

SOFTWARE CONSIDERATIONS
The building block components of a NAS solution are illustrated in figure below. This section describes the software layers in this solution stack and highlights technical considerations for software implementation.
BIOS and Drivers
In addition to the numerous vendors providing BIOS solutions for Intel processors, equipment manufacturers also develop custom BIOS versions for their particular solution. Original equipment manufacturers may also develop drivers for their own hardware (such as hard drives) or use drivers provided by Intel or other hardware manufacturers.
Operating System
The operating system (OS) manages all the software applications and hardware resources on the system. NAS appliances may use off-the-shelf desktop or server operating systems, such as Windows, Linux, or UNIX, or may utilize an embedded OS, such as Windows CE or Embedded Windows NT*. Another alternative is a real-time operating system (RTOS) such as VxWorks* or QNX*.

NAS Solution Stack
The main considerations for a NAS OS are the size and performance. Desktop operating systems are easier for the customer to implement, but take up more disk space (which means less storage) and also contain unnecessary overhead that usually degrades performance. An RTOS offers a smaller footprint and may even reside in Flash rather than on disk. Development using an RTOS allows for more direct control of the hardware, enabling optimum performance tuning. However, there is a significant investment required in developing with an RTOS. Plus, this may limit the ability to include value-added functionality, such as using the NAS device as a Web server. Embedded operating systems such as Embedded Windows NT are good alternatives because they are modular and provide tools to allow only the necessary modules to be installed. Many Linux packages also have this capability. High Availability (HA) is also becoming a key consideration for OS selection. Linux, for example, has an HA initiative underway.
Application Software and Protocols
The application software layer can be segmented into several functional areas, including services, access permissions, storage, fault tolerance, and networking. Additionally, NAS products may come with client-based tools for setup and access to the NAS device. All functional areas, aside from networking and storage, are value-added capabilities that NAS manufacturers use to differentiate their products.
File Systems
NFS: The Network File System (NFS) is an application that lets a computer user view, update, or store files on a remote computer as though they were on the userâ„¢s local hard drive. Most UNIX and Linux operating systems include NFS client and server software.
SMB: The Server Message Block (SMB) protocol allows a Windows client to access, create, and update files on a remote server. The protocol also allows the same client to access other resources such as printers and mail slots. The SMB protocol can be used over TCP/IP or other network protocols such as IPX and NetBEUI. Microsoft Windows 95 and later versions of the operating system include client and server SMB protocol support. For UNIX and Linux systems, a shareware program called Samba is available. The SMB protocol originated at Microsoft and has gone through a number of developments, eventually evolving into the CIFS standard.
CIFS: Common Internet File System (CIFS) is a standard protocol that enables programs to request files and services on remote computers on the Internet. CIFS is an open variation of SMB. Like SMB, CIFS is built upon the TCP/IP protocol. CIFS is currently the most commonly used protocol for NAS systems because it is readily available on Windows, UNIX, and Linux operating systems, and can also be used in conjunction with Novell* IPX/SPX protocols.
Networking Protocols
Networking protocols control the communication to and from the NAS device. The physical connection of a NAS is Ethernet. Because most NAS devices attempt to homogeneously communicate over the LAN, multiple network protocols are typically supported.
TCP/IP: TCP/IP (Transmission Control Protocol/Internet Protocol) is the basic communication language of the Internet. Many higher-level protocols are built on top of TCP/IP, such as Hypertext Transfer Protocol (HTTP), the File Transfer Protocol (FTP), Telnet, and the Simple Mail Transfer Protocol (SMTP).
IPX/SPX: IPX (Internetwork Packet Exchange) is a networking protocol from Novell that interconnects Novell NetWare* clients and servers. In IPX, packet acknowledgment is managed by another Novell protocol, the Sequenced Packet Exchange (SPX).
AppleTalk*: AppleTalk is a set of proprietary LAN communication protocols originally created for Apple computers. Some NAS systems support the AppleTalk protocol even though more recent Macintosh computers support TCP/IP communications.

PERFORMANCE CONSIDERATIONS
The performance of a NAS device will depend on the storage subsystem, the speed of the network connection, processing speed, and amount of system memory.
RAID-based storage subsystems offer a balance between performance and reliability. While software RAID can provide additional performance and reliability benefits relative to non-RAID implementations, it is not recommended for mission-critical data storage. Hardware-based RAID solutions result in increased performance and higher reliability.
The proposed design also uses Gigabit Ethernet controllers to enhance storage performance. Additional performance gains are possible with an intelligent Gigabit Ethernet controller with TCP/IP offload, which provides the host with additional CPU cycles for processing user requests.

SCALABILITY AND MIGRATION OPTIONS
Host Processor Options
The Pentium III processor not only allows high-performance levels to be achieved, but also brings flexibility and scalability to a NAS appliance.
Implementing dual Pentium III processors can offer a 30 to 50 percent performance gain over a single processor system (dependent on particular hardware and software implementation). Software with multiprocessing and multi-threading capability is required to achieve any performance increase. Utilizing processors of increased core frequencies, ranging from 800 MHz to 1.6 GHz, can further scale the performance of a single system to fit a specific NAS environment.
In addition, the Pentium III processor with 512 KB L2 cache is available in either a 370-pin FCPGA2 (Flip-Chip Pin-Grid Array) or a 479-ball micro-FCBGA (Flip-Chip Ball-Grid Array). The FCPGA2 package uses Socket 370, providing an easy upgrade from previous Intel Architecture processors. In contrast, users of the micro-FCBGA will benefit from the smaller form factor and improved heat dissipation. The advantage of the micro-FCBGA is apparent in dual BGA reference designs, which achieve a complete thermal solution in less than an inch total height constraint.
Storage Subsystem Options
The current protocols used for NAS are all file-level transfer mechanisms. Internet SCSI (iSCSI), however, is a block-based transfer mechanism, giving more direct access to the file systems by bypassing the OS and also removing TCP packet processing. This eliminates significant overhead associated with NFS or CIFS.
Block-based networking will eventually allow NAS devices to efficiently host large databases. For Ethernetbased network storage using iSCSI, network designers can use the Intel® Pro/1000 T IP Storage Adapter. This product uses an Intel XScale processor for offloading TCP/IP and iSCSI operations from the host.
Intel currently offers a family of RAID adapter cards (PCI and modular ROMB) optimized for different server environments. These products showcase Intelâ„¢s I/O processor technology and help system designers achieve quicker time-to-market for server RAID solutions.

SAN and NAS Fundamentals
SANs and NAS are increasingly replacing or supplementing traditional server-attached storage implementations in many data centers. As a result, organizations are realizing a wide range of benefits, including increased flexibility, easier storage deployment, and reduced overall storage costs. Although both SAN and NAS technologies can provide a competitive advantage, each is designed for specific types of environments and applications.

A basic SAN infrastructure using LAN-free data backup
to reduce network traffic

A basic NAS implementation with all data traffic flowing over the production LAN


ANTIVIRUS FOR NAS
In todayâ„¢s networked environments, high availability of data is critical to business success. To enhance availability and accelerate data retrieval, many organizations centralize tremendous volumes of data and make it available via network-attached storage systems to thousands of users across the enterprise. But, when stored data is accessible to distributed users who can download it to their local drives or even email it to others, the risk of spreading viruses rapidly throughout the enterprise becomes a dangerous threat. While it is important to protect the network perimeter, effective protection must also include vulnerable network-attached storage systems. Symantec AntiVirus for network-attached storage devices provides award-winning, unobtrusive virus protection for storage appliances at the center of enterprise networks.
Virus protection for network-attached storage devices
Network-attached storage devices handle large volumes of data, often using proprietary operating systems. As a result, standard fileserver antivirus software may not provide the necessary protection. These devices are designed for high-performance, mission-critical operations and the antivirus software that protects them must be equally fast and scalable. Because of its design as a network available service and its ability to scan high volumes of files per second, Symantec AntiVirus can help prevent network-attached storage devices from becoming a vector for spreading viruses.
Fast, scalable, and reliable
Using Symantecâ„¢s core virus detection and repair technologies, Symantec AntiVirus for network-attached storage devices provides fast, scalable, and reliable network-available antivirus services. Symantecâ„¢s core technologies scale vertically on the same server or horizontally across multiple servers and have been optimized for speed. With its ability to run simultaneously on multiple servers with minimal network impact or latency, it provides fast and scalable protection.
Award-winning antivirus technologies
Symantec AntiVirus for network-attached storage devices leverages Symantec™s award-winning technologies through Symantec AntiVirus Scan Engine to detect viruses, worms, and Trojan horses in all major file types and various compressed file formats. It can also detect malicious mobile code, such as J a v a„¢, ActiveX®, and standalone script-based threats. Symantec Anti-Virus Scan Engine takes advantage of Symantec™s key antivirus engine technologies, including Bloodhound„¢, for the heuristic detection of new or unknown viruses, and NAVEX„¢, which provides protection from new classes of viruses automatically via LiveUpdate„¢”without the need to reinstall software or interrupt virus scanning. LiveUpdate ensures that the latest definitions for detecting and eliminating viruses are delivered regularly and deployed rapidly to protect against newly identified threats.

BENEFITS OF NAS
NAS works well for organizations that need to deliver file data to multiple clients over a network. NAS appliances also function well in environments where data must be transferred over very long distances. Because most NAS requests are for smaller amounts of data, distance and network delays are less critical to data transfer. In addition, NAS appliances are relatively easy to deploy”enabling widespread distribution of NAS hosts, clients, and appliances throughout the enterprise. Properly configured, NAS provides reliable file-level data integrity, because the appliance itself handles file locking. Although deployment is fairly straightforward, organizations must be careful to ensure that appropriate levels of file security are provided during NAS appliance configuration.
A NAS appliance features the following benefits:
Open standards-based interface to data to support requests from clients based on any operating system
Scalable both in system design and by adding NAS appliances to a network
Fast data response times
Easy installation with no down time to the servers or network
Improved reliability
CHAPTER 8
Why are NAS servers faster than the normal file servers
A NAS Server is designed to provide performance file in a heterogeneous networking environment. The NAS operating system is fully optimized for file I/O activity, this makes its faster than a traditional file server which is designed to perform a perform a multitude of functions as well as file serving. Whilst a NAS serverâ„¢s OS code is optimized, it also makes the NAS server OS more reliable and better to file serving, which delivers information faster to the clients.
How reliable are NAS Servers
All the components in a NAS are designed for providing optimized data transfer to the client/ server. Because of the nature of a NAS it has a reduced component count and an optimized OS. These two things make a NAS server more reliable than a traditional file server. Many of the true NAS Servers feature full redundancy and no single point of failure. One major benefit of deploying a NAS server in place of a normal file server is less downtime. Traditional Servers from time to time need upgrading or replacing whether to add more disk drives, processors or memory. This server downtime is not always planned and when it is planned, it is at an inconvenient time or date.
By separating the storage from the server, cost savings can be made by purchasing smaller profile file servers that need less space. If the need arises to upgrade the server processor/memory the important data is held on the NAS and therefore available at all times even though the application sever is being upgraded or replaced. Many of the Network Attached Storage servers offer various levels of RAID configurations. These can be no RAID so the whole useable NAS capacity is available or RAID levels 0,1,5. This ensures that the data is protected in the event of disk failure.
Some of the higher end Network Attached Storage servers also offer high levels of redundancy against component failure. Some of the features found on these models are redundant fans, power supplies, processors, memory and motherboards.
APPLICATIONS AND USES OF NAS
Notebook/Desktop Backup
An increasing amount of valuable information is stored on local hard disks and notebook computers including Outlookâ„¢s PST files, spreadsheets, muti-media presentations, financial information etc. This information costs many times the cost of the hardware but the data is never or rarely backed up. Most NAS devices are now supplied with backup software that automatically backs up the file changes that were made since the last backup to the local NAS device when the user logs in or connects to the network. Should the notebook be stolen or desktop crash due to hard disk failure the data is now available for restore from the network.
Remote Offices
Many small remote offices have numerous client PCâ„¢s and a single server with connection over WAN to HQ. The data on this server should be backed up regularly and removed for safekeeping. Typically what happens is the person in charge of the back ups is on holiday, leaves or off sick and back ups do not get done. Should the server fail no one can now access the server for information. A way to overcome this would be to deploy a NAS device in the local office whereby user access is granted to the data and every night the data is synchronized with the remote office. This way the data is secured off-site and if the server fails users can still access the information locally.

Virtual Disk Library
With ever decreasing backup windows the cost of managing and maintaining a backup of information is becoming problematic. The normal way to increase backup performance and decrease the backup window is to buy faster higher capacity tape drives and automate the backup solution. The problem is cost, unless you have purchased a tape library that can be expanded new tape hardware will need to be bought making your old tape technology obsolete, including all the tapes with the valuable information. A simple cost effective solution could be to deploy a virtual disk library that mimics a real library with slots and cartridge capacities but is based on hard disks. Data can now be packed up at disk-to-disk speeds. When these virtual tapes are full the data can then be transferred to your real tape library and then the tapes stored for safe keeping. Should you need to increase the number of mwedia slots or require additional tape drives all that is needed if to reconfigure the Virtual Tape Library.
7x24 Backup / DR Backup
Most companies perform a backup once a day and typically at night. Should the backup fail for some reason, that night backups are never completed. This is especially critical at weekends when weekly full backups are run. Now herein lies the problem as full backups are run once a week and either incremental or differential are run daily should a server suffer failure, the backup tapes for that server would probably run into many tapes and take considerable time to restore. At best with backups being performed nightly you would loose a days work should server or disk failure occur, if you are an animation house this could run into many lakhs of rupees.
Why not every hour replicate user selected files or entire volumes from one or more source servers to one or more target NAS servers over standard network connections. By doing this the data loss suffered is minimized to the last snap shot backup.
Many companies today have a business continuity or disaster recovery plan. Normally this consists of:
Off-site location
Room full of servers
Backup tapes for restore
Communication links
Networking connections
These organizations then run periodic tests to check that they can recover information and be operating within the minimum time frame.
E-mail Archiving
In light of the recent scandals involving WorldCom, Enron and Tyco regarding the deletion of e-mails, there is currently 63% growth in storage usage attributed to email. Governments now have legislation in place regarding the storing and retrieval of e-mail and attachments for 7 years or more. Many companies have more than 200 employees and backing up either exchange or notes is a major headache for IT departments. The problems are the size of peopleâ„¢s mail boxes grow to utilize all the available disk space available, backups and restores of the whole mail system or individual mail boxes take longer due to the files types and information stored .avi, .jpg ,.mov, .doc, .xls, .mp3 .pst etc.
Why not deploy a NAS server and automatically migrate aged files from the main mail server to the NAS. The user is unaware this has happened as he still sees the files as he would normally with the attachments. By doing this the backups on the mail server will be considerably quicker and in the event of failure the server can be restored much faster.
Reducing Networking Traffic
If you have users within your organization that regularly transfer image files around the network i.e. Movies, graphics, animations, pictures. A solution is to segment the users using a network switch and install a NAS device on their local network segment.
Consolidating servers
A server consists of 4 key components “storage, processor, memory and OS. When you buy a server you would pay for the disk drives, CD/DVD drives, SCSI controllers, RAID controllers, processors, memory, case, tape device and OS license. These servers normally act as file & print servers or run applications. When the server becomes fully populated with disks another server is bought and so the cycle continues. These new servers sit alongside the older server or are complete replacement models. The valuable information stored on these servers then has to be moved/backed up and migrated to the new server all this takes considerable time, looking for service packs, software license numbers, patches, checking the new server will run the same applications as the old etc.
Why not deploy a NAS Server for disk storage or to run applications. These can be easily added and integrated in your existing server framework with the minimum of fuss and no server downtime and be remotely managed via browser. Should you reach the capacity of your NAS Server create a virtual storage pool. For example, you can pool multiple NAS Servers together. Data that is not accessed frequently can be automatically migrated off of critical front-line servers to NAS Server, freeing up overloaded servers for application use. When needed, users have immediate and transparent access to all of their critical stored data with no administrator intervention.
Archival Storage
Traditionally information has been stored on magnetic media, typically in a RAID system. This provides a level of redundancy and fast access to information. On most RAID systems only about 20% of this information is active, the remaining 80% infrequently accessed. When the RAID system is full of information the IT manager has some options to choose:
Install new hard disks “ This creates a problem the server needs to be taken offline whilst the new disks are added formatted and partitioned.
Archive the information “ The problem when Archiving information is what are you actually going to archive Do you send round a memo asking people to let the IT person know what files they frequently use or access The answer is NO! So this is an ineffective way of moving files.
Just delete or copy the files to tape and keep a copy “ This is great if no one wanted to access old information, but in the real world, people will always want to refer to an aged document.
By having RAID systems with data that is infrequently accessed can cause the tape backup system to overrun or span multiple tapes as well as causing unnecessary wear and tear on the drives by backing up the same old files every night.
By implementing a HSM Software solution the user will free up valuable disk space, reduce the backup window, migrating the data to a NAS Server will be able to manage the data storage in a more flexible way.
Software Distribution
How often do businesses need to send software updates to remote offices or stores Some of these updates maybe pricelists, brochure changes, service packs or anti-virus software updates. By having a centralized NAS Server updates can be put on the main office NAS and then these updates can be synchronized to the remote offices for u se. The software works with one-to-many or many-to-one. Another use is estate agents have lots personnel and important data relating to house sales, this information is usually held on the various PCâ„¢s around the office. If you install a small capacity NAS Server, every night this information can be synchronized with the remote office. Should anything happen to the office PCâ„¢s the data is still secured remotely.

APPLICATIONS FOR NAS
There are an estimated 5 million NT 4 servers in the world today with the support ending in 2003, by moving the information from these file servers to NAS Servers will increase productivity and support.
File/Print server
Application specific server
Video Imaging
Graphical image store
Centralized heterogeneous file sharing
File system mirroring
Snap shot critical data
Replacement of traditional backup methods
Medical imaging
CAD/CAM
Portable centralized storage for offsite project and implimentations

ADVANTAGES OF NAS
Decreased IT Staff Costs
On the front end, businesses welcome extreme amounts of information and strive to manipulate it for use in real time. On the back end, IT professionals, with their current infrastructures, scramble to accommodate the exponentially increasing data burden. General-purpose servers, especially, require large amounts of skilled personnel time to solve storage and file access challenges.
In contrast, a NAS device requires little IT staff time and effort. Management is accomplished through a graphical user interface (GUI) in a Web browser, which enables NAS access from anywhere on the network. Since a NAS filer is pre-configured to support specific file-serving needs, administration is simplified, and this ease of use results in fewer operator errors. Also, because more capacity can be managed per administrator with NAS than is possible with general-purpose server storage activity, the total cost of ownership is lower.
Scale Fast, Without Downtime
Dot-coms and other rapidly scaling companies endeavor to make sure their IT infrastructures keep pace with their dynamic business realities. Building on the structure of your general server or servers may be required in some business areas. But burdening these servers with escalating storage needs can be ineffective and run counter to your accelerated business practices. As you add capacity for your general-purpose server, you'll face downtime. When you bring the system down to increase its storage, your business applications will be unavailable, which may slow-if not halt-productivity.
On the other hand, expanding storage with NAS is simple and nonintrusive. You can install a new filer within 15 minutes as opposed to hours or days required to install or add traditional storage. More advanced NAS devices can increase storage on-the-fly, eliminating the need for you to add another node on your network. This means your users access what they need when they need it, responding in real time to a marketplace that demands immediate action.
Relief for Your Server
A NAS filer helps by offloading tedious and bandwidth-consuming file serving tasks from your server. This allows your server to use its power to process your data with improved availability and performance. Have you checked your general-purpose server's workload lately If it is handling file-serving activities, chances are it is handling too much. You face increased risk of latency when your general-purpose server must complete high-priority file serving tasks while handling applications, electronic mail, and a myriad of other critical business tasks.
Multi-OS Connectivity and Data-Sharing
Whether your company is busy merging or acquiring, or simply growing, you will no doubt face the demands of a heterogeneous operating environment. A NAS device can answer this challenge with its capability to serve two chief operating system camps: NFS (UNIX) and CIFS (Microsoft Windows). One of the undeniable strengths of NAS is its capacity to support these protocols and allow for cross-platform data sharing. This is an increasingly important attribute as the business usage of data-intensive application files such as digital media (audio, video, and photography) becomes more common.
Leveraging Existing Infrastructure
By adding NAS nodes to your network, you can leverage your network investment and your current network administration skills. NAS can be deployed on your network anywhere it is needed. It also can be integrated with larger management tools, like Microsoft Management Console, Tivoli, and HP Openview, allowing you to maximize your use of these products. And NAS does not require costly network operating system (NOS) licenses.
Often, IT centralization is asked to simplify responsibilities and conserve company efforts, but it accomplishes neither if remote branch and satellite offices must operate without IT support. NAS can help you realize the intent of centralization by allowing you to add storage in a remote office and manage it via the Web-based GUI from anywhere on your network-including your central/home office. This means you can reap higher performance from existing infrastructure at the remote office and keep management "at home."
Transparent Backup
Another benefit of NAS is its transparent backup activities. Filer backup can be completed without affecting the performance of your general-purpose or application servers. Your CPU does not have to calculate what to back up and when. Simply direct your filer to complete backup at a specific time and it will use industry-standard procedures to complete this task.
FUTURE SCOPE
NAS Solutions for Tomorrowâ„¢s Business Issues
IDC predicts that by 2003, more than $6.5 billion will be spent annually on NAS storage solutions. (Source: Taming the Storage Growth Beast with Network-Attached Storage (NAS), ¨ 2000, International Data Corporation.) The analyst group believes the demands of Internet service providers, application service providers, and dot-coms for reliable, cost-effective, and rackable systems will help drive the proliferation of NAS solutions.

CONCLUSION
Focusing processing power solely on file service and storage, NAS filers can serve any business or technology workgroup-from software design to CAD to service providers/dot-coms to engineering-that requires low cost, scalability, and high-performance in a file server. NAS also can work in tandem with your SAN environment, handling network file serving needs while the SAN tackles back-end storage tasks. Unobtrusive and accommodating, filers meld with your existing infrastructure and facilitate data sharing across heterogeneous operating environments. The Internet revolution will push NAS into mainstream. The need for storage connectivity and improved reliability will demand more than other storage media can produce

REFERENCES
¢ Complete Reference of Storage Networks by Robert Spalding
¢ i.t magazine
¢ bitpipe.com
¢ intel.com

ACKNOWLEDGEMENT
I express my sincere gratitude to Dr. Agnisarman Namboodiri, Head of Department of Information Technology and Computer Science , for his guidance and support to shape this paper in a systematic way.
I am also greatly indebted to Mr. Saheer H. and
Ms. S.S. Deepa, Department of IT for their valuable suggestions in the preparation of the paper.
In addition I would like to thank all staff members of IT department and all my friends of S7 IT for their suggestions and constrictive criticism.

CONTENTS
1. INTRODUCTION¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦.. 1
2. NETWORK STORAGE CONCEPTS¦¦¦¦¦¦¦¦¦¦ 3
3. WHAT IS NAS ¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦. 6
4. NAS BLOCK DIAGRAM¦¦¦¦¦¦¦¦¦¦¦¦¦¦.. 7
5. FUNCTIONAL DESCRIPTION¦¦¦¦¦¦¦¦¦¦¦¦.. 8
6. SOFTWARE CONSIDERATIONS¦¦¦¦¦¦¦¦¦¦¦ 12
7. PERFORMANCE CONSIDERATONS¦¦¦¦¦¦¦¦¦.. 16
8. SCALABILITY AND MIGRATION OPTIONS¦¦¦¦¦¦. 17
9. NAS AND SAN¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦ 19
10. ANTIVIRUS FOR NAS¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦ 21
11. BENEFITS OF NAS¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦.. 23
12. APPLICATIONS AND USES OF NAS¦¦¦¦¦¦¦¦¦¦ 25
13. APPLICATIONS FOR NAS¦¦¦¦¦¦¦¦¦¦¦¦¦¦. 31
14. ADVANTAGES OF NAS¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦ 32
15. FUTURE SCOPE¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦. 35
16. CONCLUSION ¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦ 36
17. REFERENCES¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦.. 37
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ABSTRACT
Information Technology (IT) departments are looking for cost-effective storage solutions that can offer performance, scalability, and reliability. As users on the network increase and the amounts of data generated multiply, the need for an optimized storage solution becomes essential. Network Attached Storage (NAS) is becoming a critical technology in this environment. The benefit of NAS over the older Direct Attached Storage (DAS) technology is that it separates servers and storage, resulting in reduced costs and easier implementation. As the name implies, NAS attaches directly to the LAN, providing direct access to the file system and disk storage. Unlike DAS, the application layer no longer resides on the NAS platform, but on the client itself. This frees the NAS processor from functions that would ultimately slow down its ability to provide fast responses to data requests. In addition, this architecture gives NAS the ability to service both Network File System (NFS) and Common Internet File System (CIFS) clients. Also this allows the IT manager to provide a single shared storage solution that can simultaneously support both Windows*-and UNIX*-based clients and servers. In fact, a NAS system equipped with the right file system software can support clients based on any operating system.
CONTENTS
1. HISTORY OF NETWORK ATTACHED STORAGE ¦¦¦¦¦¦¦¦.. 3
1.1 INTRODUCTION
1.2 BACKGROUND
2. STORAGE TOPOLOGIES ¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦.. 5
2.1 TYPES OF STORAGE TOPOLOGIES
2.2 ADVANTAGES OF INTELLIGENT STORAGE
2.3 DIRECT ATTACHED STORAGE [DAS]
2.4 STORAGE AREA NETWORK [SAN]
2.5 NETWORK ATTACHED STORAGE [NAS]
3. COMPARISON BETWEEN STORAGE SYSTEMS ¦¦¦¦¦¦¦¦.. 10
3.1 NAS vs. TRADITIONAL FILE SERVERS OR DAS
3.2 NAS vs. SAN
3.3 NETWORK STORAGE RECAP
4. NAS DESCRIPTION ¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦... 14
4.1 What Is NAS
4.2 DETAILED DESCRIPTION ON NAS
5. FURTHER TOPICS OF NAS ¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦ 18
5.1 CONCEPT OF RAID
5.2 RAID LEVELS
5.3 NAS PROTOCOLS
5.4 NAS HEADS OR GATEWAYS
5.5 NAS BENEFITS, DRAWBACKS AND USES
6. CONCLUSION ¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦. 25
7. REFERENCES ¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦. 26
ACKNOWLEDGMENT
On presenting the report on Network Attached Storage, I feel greatly to express my humble feelings of thanks to one and all who have helped me directly or indirectly in the successful completion of the seminar and presentation.
I am grateful to my institution YELLAMMA DASAPPA Institute Of Technology and Department of Electronics & Communication and Engineering for imparting me the knowledge with which I can do my best.
I am grateful to Dr. K.V.S Ananda Babu, Principal, CMRIT, Bangalore for providing me congenial environment to work in.
I would like to thank my guide Prof. G Indumathi , HOD, Dept of ECE, who has helped me a lot in making this seminar and presentation report and for her continuous encouragement, guidance and moral support throughout the seminar and presentation work.

Finally, I would like to thank all Lecturers of Dept of ECE, all my friends, who with their constant and creative criticism, made me to maintain standards throughout my endeavor to complete this seminar and presentation work.
1. HISTORY OF NETWORK ATTACHED STORAGE
1.1 INTRODUCTION
You can never have enough storage, whether a bigger house to store your belongings or more hard disk space to store your data on a network. However dedicated network devices provide affordable, easy access to data. Several new methods of utilizing computer networks for data storage have emerged in recent years. One popular approach, Network Attached Storage (NAS), allows homes and businesses to store and retrieve large amounts of data more affordably than ever before.
1.2 BACKGROUND

Historically, floppy drives have been widely used to share data files, but today the storage needs of the average person far exceed the capacity of floppies. Businesses now maintain an increasingly large number of electronic documents and presentation sets including video clips. Home computer users, with the advent of MP3 music files and JPEG images scanned from photographs, likewise require greater and more convenient storage.

Central file servers use basic client/server networking technologies to solve these data storage problems. In its simplest form, a file server consists of PC or workstation hardware running a network operating system (NOS) that supports controlled file sharing (such as Novell NetWare, UNIX or Microsoft Windows). Hard drives installed in the server provide gigabytes of space per disk, and tape drives attached to these servers can extend this capacity even further.
File servers boast a long track record of success, but many homes, workgroups and small businesses cannot justify dedicating a fully general-purpose computer to relatively simple data storage tasks. So, Network-attached storage was introduced with the early file sharing Novell's NetWare server operating system and NCP protocol in 1983. In the UNIX world, Sun Microsystems' 1984 release of NFS allowed network servers to share their storage space with networked clients. 3Com's, 3Servers and 3+Share software was the first purpose-built servers (including proprietary hardware, software, and multiple disks) for open systems servers, and the company led the segment from 1985 through the early 1990s. 3Com and Microsoft would develop the LAN manager software and protocol to further this new market. Inspired by the success of file servers from Novell, IBM, and Sun, several firms developed dedicated file servers. While 3server was among the first firms to build a dedicated NAS for desktop operating systems, Auspex Systems was one of the first to develop a dedicated NFS server for use in the UNIX market. A group of Auspex engineers split away to create the integrated Network Appliance "filer", which supported both Windows and UNIX, in the early 1990s, starting the market for proprietary NAS arrays.
STORAGE TOPOLOGIES
2.1 TYPES OF STORAGE TOPOLOGIES
Direct Attached Storage [DAS].
Storage Area Network [SAN].
Network Attached Storage [NAS].
2.2 ADVANTAGES OF INTELLIGENT STORAGE
Cost of Bandwidth
Cost of Space
Cost of Storage System v. Cost of Disks
Physical Repair, Number of Spare Parts
Cost of Processor Complexity
Cluster advantages: dependability, scalability
2.3 DIRECT ATTACHED STORAGE [DAS]
The most basic method of attaching storage to a network is a one-to-one direct connection to a network server. Disk arrays are typically connected to a server using SCSI connectors and then shared out to network users. Although this method is certainly the easiest to implement, it does not scale very gracefully as storage needs grow. As a DAS system grows it becomes exponentially unwidely, costly to backup. manage and maintain and unreliable. Additionally, administration of DAS can become more difficult with the potential proliferation of disparate systems.
DIRECT ATTACHED STORAGE (DAS) TOPOLOGY
2.4 STORAGE AREA NETWORK [SAN]

A SAN is a network of storage devices that are connected to each other and to a server, or cluster of servers, which act as an access point to the SAN. In some configurations a SAN is also connected to the network. SAN's use special switches as a mechanism to connect the devices. These switches, which look a lot like a normal Ethernet networking switch, act as the connectivity point for SAN's. Making it possible for devices to communicate with each other on a separate network brings with it many advantages. Consider, for instance, the ability to back up every piece of data on your network without having to 'pollute' the standard network infrastructure with gigabytes of data. This is just one of the advantages of a SAN which is making it a popular choice now a days.
Storage Area Network (SAN) Topology
2.5 NETWORK ATTACHED STORAGE [NAS]
Network-attached storage (NAS) is the name given to dedicated data storage technology that can be connected directly to a computer network to provide centralized data access and storage to heterogeneous network clients.
A typical NAS solution, where all traffic flows over the production LAN.
Network-attached storage (NAS) is hard disk storage that is set up with its own network address rather than being attached to the department computer that is serving applications to a network's workstation users. By removing storage access and its management from the department server, both application programming and files can be served faster because they are not competing for the same processor resources. The network-attached storage device is attached to a local area network (typically, an Ethernet network) and assigned an IP address. File requests are mapped by the main server to the NAS file server.
The growing market for network storage is a result of the exploding demand for storage capacity in our increasingly internet-dependent world and its tight labor market. Storage area networks (SAN) and network attached storage (NAS) are two proven approaches to networking storage technically including a file system in a storage subsystem differentiates NAS which has one from SAN, which doesnâ„¢t in practice, however it is often NASâ„¢ s close association with ethernet hardware
3. COMPARISON BETWEEN STORAGE SYSTEMS
3.1 NAS vs. TRADITIONAL FILE SERVERS OR DAS
Proponents of NAS claim that NAS technology provides these advantages over traditional file servers:
Lower cost
Better Security
Higher Availability (less downtime)
Easier to use and administer
NAS differs from the traditional file serving and Direct Attached Storage in that the operating system and other software on the NAS unit provide only the functionality of data storage, data access and the management of these functionalities. Furthermore, the NAS unit does not limit clients to only one file transfer protocol. NAS systems usually contain one or more hard disks, often arranged into logical, redundant storage containers or RAIDs(redundant arrays of independent disks), as do traditional file servers. NAS removes the responsibility of file serving from other servers on the network and can be deployed via commercial embedded units or via standard computers running NAS software.
NAS products improve on traditional file servers generally through the principle of simplification. By stripping out all of the unnecessary capabilities of a general purpose server -applications, services or daemons, and hardware peripherals -a NAS device becomes less prone to system "crashes" and security attacks. When a problem does occur, a NAS system can be diagnosed and rebooted much faster due to its lower level of complexity.
NAS products also generally hide the operating system personality of the device. Whereas Windows, UNIX and NetWare file servers each demand specific protocol support on the client side, NAS systems strive for greater operating system independence of clients.

Opponents of NAS emphasize that traditional file servers have a proven record of success compared to this new breed of "upstart" NAS systems. High-end file systems also contain more processing power than a NAS device, giving servers a performance edge (in terms of transactions or I/O per second rates) over NAS.

The new breed of NAS networking products has succeeded in providing a reasonable alternative to traditional file servers in client/server networks. Entry-level NAS products containing 20-50 gigabytes of storage can be purchased for $500 (USD) or less, whereas mid-range and high-end NAS systems can run in the tens of thousands of dollars. Besides cost, a NAS promises reliable operation and easy management.
3.2 NAS vs. SAN
At a high level, Storage Area Networks (SAN s) serve the same purpose as a NAS system. A SAN supplies data storage capability to other network devices. Traditional SAN s differed from traditional NAS in several ways. Specifically, SAN s often utilized Fibre Channel rather than Ethernet, and a SAN often incorporated multiple network devices or "endpoints" on a self-contained or "private" LAN, whereas NAS relied on individual devices connected directly to the existing public LAN. The traditional NAS system is a simpler network storage solution, effectively a subset of a full SAN implementation.

The distinction between NAS and SAN has grown fuzzy in recent times, as technology companies continue to invent and market new network storage products. Today's SAN s sometimes use Ethernet, NAS systems sometimes use Fibre Channel, and NAS systems sometimes incorporate private networks with multiple endpoints. Fibre Channel is a technology used to interconnect storage devices allowing them to communicate at very high speeds (up to 10Gbps in future implementations).The primary differentiator between NAS and SAN products now boils down to the choice of network protocol. SAN systems transfer data over the network in the form of disk blocks (fixed-sized file chunks, using low-level storage protocols like SCSI) whereas NAS systems operate at a higher level with the file itself.
3.3 NETWORK STORAGE RECAP

Storage area network

Network attached storage
Connectivity
Fibre Channel, iSCSI
IP
Data access method
Block
File
Key requirement Deterministic performance, support for high-transaction applications
Sharing, collaboration
Type of applications
OLTP, data warehousing, ERP, SCM, etc
File and print server consolidation, product design, engineering
Typical market segment
Large businesses, midsize, SMBs “ iSCSI
All
4. NAS DESCRIPTION
4.1 What Is NAS
NAS challenges the traditional file server approach by creating systems designed specifically for data storage. Instead of starting with a general-purpose computer and configuring or removing features from that base, NAS designs begin with the bare-bones components necessary to support file transfers and add features "from the bottom up."
General structure of Network Attached Storage [NAS].
Like traditional file servers, NAS follows a client/server design. A single hardware device, often called the NAS box or NAS head, acts as the interface between the NAS and network clients. These NAS devices require no monitor, keyboard or mouse. They generally run an embedded operating system rather than a full-featured NOS. One or more disk (and possibly tape) drives can be attached to many NAS systems to increase total capacity. Clients always connect to the NAS head, however, rather than to the individual storage devices. Clients generally access a NAS over an Ethernet connection. The NAS appears on the network as a single "node" that is the IP address of the head device.
A NAS can store any data that appears in the form of files, such as email boxes, Web content, remote system backups, and so on. Overall, the uses of a NAS parallel those of traditional file servers. NAS systems strive for reliable operation and easy administration. They often include built-in features such as disk space quotas, secure authentication, or the automatic sending of email alerts should an error be detected. The advantage of NAS is that it concentrates on managing the file requests and storage; it is not sharing processor power with applications and general users. This also means that it is faster to reboot if problems occur. Because Network speeds are now as fast as internal server processing, NAS is as fast as DAS.
4.2 DETAILED DESCRIPTION ON NAS
Network Attached Storage, or NAS, is a data storage mechanism that uses special devices connected directly to the network media. These devices are assigned an IP address and can then be accessed by clients via a server that acts as a gateway to the data, or in some cases allows the device to be accessed directly by the clients without an intermediary.

The beauty of the NAS structure is that it means that in an environment with many servers running different operating systems, storage of data can be centralized, as can the security, management, and backup of the data. An increasing number of companies already make use of NAS technology, if only with devices such as CD-ROM towers (stand-alone boxes that contain multiple CD-ROM drives) that are connected directly to the network).
Some of the big advantages of NAS include the expandability; need more storage space, add another NAS device and expand the available storage. NAS also bring an extra level of fault tolerance to the network. In a DAS environment, a server going down means that the data that that server holds is no longer available. With NAS, the data is still available on the network and accessible by clients. Fault tolerant measures such as RAID, can be used to make sure that the NAS device does not become a point of failure.
Generally NAS are used, in order the high up would wind at installation and administration of a dedicated file server to go around. A NAS is usually to install simply, easily scalable, to administrater simply. Since the functions with the targeted application to be very specifically co-ordinated can. In this way error causes are avoided from the beginning e.g. due to more extensive and for the special targeted application than NAS of unnecessary configuration options. File-based services such as NFS or SMB/CIFS represent the kernel function. Therefore NAS systems are called Filer often briefly.
Network-attached storage consists of hard disk storage, including multi-disk RAID systems, and software for configuring and mapping file locations to the network-attached device. Network-attached storage can be a step toward and included as part of a more sophisticated storage system known as a storage area network.

NAS software can usually handle a number of network protocols, including Microsoftâ„¢ s Internetwork Packet exchange and NetBEUI, Novell's Netware Internetwork Packet exchange, and Sun Microsystemsâ„¢ Network File System. Configuration, including the setting of user access priorities, is usually possible using a Web browser. A NAS can have either own fixed disk (NAS Appliance) or to a Storage Area network (SAN) be attached (NAS head, NAS head) and over it memory of attached storage systems to use.
A network-attached storage (NAS) device is a server that is dedicated to nothing more than file sharing. NAS does not provide any of the activities that a server in a server-centric system typically provides, such as e-mail, authentication or file management. NAS allows more hard disk storage space to be added to a network that already utilizes servers without shutting them down for maintenance and upgrades. With a NAS device, storage is not an integral part of the server. Instead, in this storage-centric design, the server still handles all of the processing of data but a NAS device delivers the data to the user. A NAS device does not need to be located within the server but can exist anywhere in a LAN and can be made up of multiple networked NAS devices.
NAS uses file-based protocols such as NFS (popular on UNIX systems) or SMB (Server Message Block) used with MS Windows systems. Contrast NAS' s file-based approach and use of well-understood protocols with Storage Area Network (SAN) which uses a block-based approach and generally runs over SCSI over Fibre Channnel or iSCSI (There are other SAN protocols as well, such as ATA over ethernet and HyperSCSI, which however are less common.
Minimal-functionality or stripped-down operating systems are used on NAS computers or devices which run the protocols and file applications that provide the NAS functionality. A "leaned-out" FreeBSD is used in FreeNAS for example, which is open source NAS software meant to be deployed on standard computer hardware. Commercial embedded devices and consumer "network appliances" may use closed source operating systems and protocol implementations.

Network-attached storage is one way around the slowdowns and service interruptions that occur in a conventional file server model.
5.FURTHER TOPICS OF NAS
5.1 CONCEPT OF RAID
DEFINITION: Redundant Array of Independent Disks [RAID], A disk subsystem that is used to increase performance or provide fault tolerance or both. RAID uses two or more ordinary hard disks and a RAID disk controller. In the past, RAID has also been implemented via software only.
Small and Large RAID subsystems come in all sizes from desktop units to floor-standing models. Stand-alone units may include large amounts of cache as well as redundant power supplies. Initially used with servers, desktop PCs are increasingly being retrofitted by adding a RAID controller and extra IDE or SCSI disks. Newer motherboards often have RAID controllers.Disk Striping
RAID improves performance by disk striping, which interleaves bytes or groups of bytes across multiple drives, so more than one disk is reading and writing simultaneously.
Mirroring and Parity
Fault tolerance is achieved by mirroring or parity. Mirroring is 100% duplication of the data on two drives (RAID 1). Parity is used to calculate the data in two drives and store the results on a third (RAID 3 or 5). After a failed drive is replaced, the RAID controller automatically rebuilds the lost data from the other two. RAID systems may have a spare drive (hot spare) ready and waiting to be the replacement for a drive that fails. The parity calculation is performed in the following manner: a bit from drive 1 is XOR' d with a bit from drive 2, and the result bit is stored on drive 3 (see OR for an explanation of XOR).
5.2 RAID LEVELS
RAID 0 - Speed (Widely Used)
RAID level 0 is disk striping only, which interleaves data across multiple disks for performance. Widely used for gaming, RAID 0 has no safeguards against failure.
RAID 1 - Fault Tolerance (Widely Used)
Uses disk mirroring, which provides 100% duplication of data. Offers highest reliability, but doubles storage cost. RAID 1 is widely used in business applications.
RAID 2 - Speed
Instead of single bytes or groups of bytes (blocks), bits are interleaved (striped) across many disks. The Connection Machine used this technique, but this is rarely used because 39 disks are required.
RAID 3 - Speed and Fault Tolerance
Data are striped across three or more drives. Used to achieve the highest data transfer, because all drives operate in parallel. Using byte level striping, parity bits are stored on separate, dedicated drives.
RAID 4 - Speed and Fault Tolerance
Similar to RAID 3, but uses block level striping. Not often used.
RAID 5 - Speed and Fault Tolerance (Widely Used)
Data are striped across three or more drives for performance, and parity bits are used for fault tolerance. The parity bits from two drives are stored on a third drive and are interspersed with user data. RAID 5 is widely used in servers.
RAID 6 - Speed and Fault Tolerance
Highest reliability because it can recover from a failure of two disks, but not widely used. Similar to RAID 5, but performs two different parity computations or the same computation on overlapping subsets of the data.
RAID 10, RAID 100 - Speed and Fault Tolerance
RAID 10 is RAID 1 + 0. The drives are striped for performance (RAID 0), and all striped drives are duplicated (RAID 1) for fault tolerance.RAID 100 is RAID 10 + 0. It adds a layer of striping on top of two or more RAID 10 configurations for even more speed.
5.3 NAS PROTOCOLS
Communication with a NAS head occurs over TCP/IP. More specifically, clients utilize any of several higher-level protocols (application or layer seven protocols in the OSI model) built on top of TCP/IP.
The two application protocols most commonly associated with NAS are Sun Network File System (NFS) and Common Internet File System (CIFS). Both NFS and CIFS operate in client/server fashion. Both predate the modern NAS by many years; original work on these protocols took place in the 1980s.
Many NAS systems also support Hypertext Transfer Protocol (HTTP). Clients can often download files in their Web browser from a NAS that supports HTTP. NAS systems also commonly employ HTTP as an access protocol for Web-based administrative user interfaces.
5.4 NAS HEADS OR GATEWAYS
The hardware that performs the NAS control functions is called a NAS head or NAS gateway. The clients always connect to the NAS head, as it is the NAS head is addressable on the network. A NAS head is usually a discrete hardware device that is independent of the storage devices and contains an imbedded operating system that does not need a keyboard, mouse or monitor. A storage administrator accesses the appliance and manages the disk resources from a remote console. Disks and in some cases tape drives are attached to the NAS head for capacity. NAS Heads are also sometimes called NAS appliances, based on the ideas that NAS is a commodity item like a toaster or washing machine.
A NAS head may also refers to a NAS which does not have any on-board storage, but instead connects to a SAN. In effect, it acts as a translator between the file-level NAS protocols (NFS,CIFS,etc.) and the block-level SAN protocols (Fibre Channel, iSCSI). Thus it can combine the advantages of both technologies
5.5 NAS BENEFITS
Storing Unstructured data: Network Attached Storage is a more appropriate solution for storing and managing unstructured type of data, from a cost and usability perspective. NAS appears to the user as a normal network drive or server, but in fact it can be centralized and store many terabytes of data.
Computer Network support: The NAS Server comes network ready and connects to your Ethernet hub. It's truly plug-and-play. The Server networks and manages hard disks on Windows NT/200/2003, Apple and UNIX networks concurrently. It simultaneously supports multiple protocols. The NAS8200 systems come with dual Gigabit Ethernet interfaces and the NAS8100 systems have optional Gb Ethernet interfaces to the network.
RAID Data Protection: The NAS Server supports RAID 0 (Striping), RAID 1 (Mirroring) and RAID 5. The NAS system supports hot-swap EIDE drives.
Storage/application host independence: Multiple application servers and/or clients can directly access needed information. This yields a high degree of flexibility, without having to rearrange hardware.
The appliance approach: The storage server can be streamlined and optimized to do one thing - serving data - very well.
Leveraging existing Expertise: since it uses standard technologies that users are already familiar with, along with their existing infrastructure).
Easy Seamless Sharing: The NAS Server operates with unmatched simplicity right out of the carton. The server appears in the network neighborhood and can be mapped to a single drive letter. This is an independent network appliance, its operation neither affects nor is impacted by the network file server. The NAS Server appears as a server on your network, and can be accessed as such. Hundreds of users can simultaneously access the hard drives with unmatched ease and simplicity.
Easy to install and manage: Installation is very easy. Just plug in the Ethernet cable, plug in the power cable and turn on the unit. There's no software to load. A quick installation wizard, and a Web Browser are used to configure the NAS Server. It allows you to set up security by individual and group. Your server is never out of date - you can download the latest firmware as it becomes available.
Built to user requirements: We will configure a system to your requirements. Select - capacity, tower or rack cabinet, EIDE drives, RAID or just plain drives, hot-swap drives, hot-swap power.
Other Benefits: NAS helps improve the performance of your file stores and ensures that users continue to have reliable access to their files for as long as necessary. This in turn helps to enhance user satisfaction and boost productivity. NAS is useful for more than just general centralized storage provided to client computers in environments with large amounts of data. NAS can enable simpler and lower cost systems such as load-balancing and fault-tolerant email and web server systems by providing storage services.
DRAWBACKS
Due to the multiprotocol, and the reduced CPU and OS layer, the NAS has its limitations compared to the DAS/SAN systems. If the NAS is occupied with too many users, too many I/O operations, or CPU processing power that is too demanding, the NAS reaches its limitations. A server system is easily upgraded by adding one or more servers into a cluster, so CPU power can be upgraded, while the NAS is limited to its own hardware, which is in most cases not upgradeable.
Certain NAS devices fail to expose well-known services that are typical of a file server, or enable them in a way that is not efficient. Examples are: ability to compute disk usage of separate directories, ability to index files rapidly (locate), ability to mirror efficiently with rsync. One may still use rsync, but through an NFS or CIFS client; that method fails to enumerate huge file hierarchies at the nominal speed of local drives and induces considerable network traffic.
It should be noted that NAS is effectively a server in itself, with all major components of a typical PC “ a CPU, motherboard, RAM, etc. “ and its reliability is a function of how well it is designed internally. A NAS without redundant data access paths, redundant controllers, redundant power supplies, is probably less reliable than Direct Attached Storage (DAS) connected to a server which does have redundancy for its major components.
USES
NAS is useful for more than just general centralized storage provided to client computers in environments with large amounts of data.
NAS can enable simpler and lower cost systems such as load-balancing and fault-tolerant email and web server systems by providing storage services. The potential emerging market for NAS is the consumer market where there is a large amount of multi-media data. Such consumer market appliances are now commonly available. Unlike their rackmounted counterparts, they are generally packaged in smaller form factors.
The price of NAS appliances has plummeted in recent years, offering flexible network-based storage to the home consumer market for little more than the cost of a regular USB or FireWire external hard disk. Many of these home consumer devices are built around ARM, PowerPC or MIPS processors running an embedded Linux operating system.
6.CONCLUSION
Storage systems are becoming the dominant investment in corporate data centers and a crucial asset in e-commerce, making the rate of growth of storage a strategic business problem and a major business opportunity for storage vendors. In order to satisfy user needs, storage systems should consolidate resources, deploy quickly, be centrally managed, be highly available, and allow data sharing. It should also be possible to distribute them over global distances, make them secure against external and internal abuse, and scale their performance with capacity. Putting storage in specialized systems and accessing it from clients across a network provides significant advantages for users. Moreover, the most apparent difference between the NAS and SAN versions of network storage”use of Ethernet in NAS and Fibre Channel in SAN”is not a core difference and may soon not even be a recognizable difference. Instead, we may have NAS servers that look like disks, disks that connect to and operate on Ethernet, arrays of disk bricks that, as far as the user is concerned, function as one big disk, and arrays of smart disks that verify every command against the rights of individual
users.
7.REFERENCES
1. wikipedia.com.
2. brocade.com.
3. storageadmin.com.
4. netapp.com.
5. perforce.com.
hey
please read topicideashow-to-network-attached-storage--5661 and topicideashow-to-network-attached-storage-nas to get more technical information about Network Attached Storage (NAS)
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