Are you facing the challenge of preserving data? Here are a few guidelines for choosing an appropriate Network Attached Storage (NAS). by Mahesh Rathod & Suryakant Naik

Data is the most valuable resource for any organization. This makes it imperative for IT managers to address the data storage and management needs of an enterprise. Data needs to be stored securely and made available round the clock.

Enterprise data storage started with server storage where each server had its own built-in, dedicated storage. Then came DAS (Direct Attached Storage), which utilizes a dedicated storage server and contains a file system to manage storage. These technologies however gave rise to performance issues when many servers or hosts were accessing the same DAS.

NAS (Network Attached Storage) and SAN (Storage Area Network) were mainly developed to address the limitations of these technologies.

Understanding NAS
NAS is based on mature technologies. It is platform and OS independent and frees up processing power for key applications running on the server, as it enables clients to access storage across the network. NAS enables storage to be available independent of server availability.

NAS is based on open networking standards. There are two true network standards for accessing remote data that have been broadly implemented by virtually all Unix and Windows system vendors. NFS (Network File System) is the de-facto standard for Unix while CIFS (Common Internet File System) is the standard for all flavors of the Windows operating system. As a result of these broadly accepted standards for network data access, storage devices that serve data directly over a network (called Network Attached Storage or NAS servers) are far easier to connect and manage than DAS devices.

Most NAS servers have their own file system, usually a thin OS that performs the task of efficiently managing file services. These thin OSs are mostly stripped down version of Unix, Linux or Windows. NAS is the only form of storage that optimally supports both NFS and CIFS network file system protocols for sharing storage between Unix and Windows hosts. It is important to note that about 75 percent of users today share data between Unix and NT, making these type of applications a key differentiator between DAS and NAS.

The works
In NAS, the client I/O requests are passed over a network before arriving at the disk where the desired data resides. Both the requested and the returned data pass through many layers of software as the I/O makes its way from application to disk and back again. It is important to remember that clients send requests for remotely stored files over the network to the NAS server. The NAS server returns the file to the client after translating it into block addresses, retrieving the data from disk and repackaging the data for transmission over the network to the requesting client.

Evaluation parameters
The selection of the right NAS solution can be based on the following selection criteria:

Processors: Workgroup and lower end organization-level NAS should have a single processor with a clock frequency ranging from 300 MHz to 800 MHz for network processing, file and storage processing. The main benefit of a single processor is the low cost and drawback being the limited scalability in terms of capacity and performance.

High-end enterprise class NAS should come with two or more processors (minimum 800 MHz) based on whether they follow symmetric multiprocessing architecture or functional multiprocessing architecture.

Memory: Workgroup or organization-level NAS should have minimum of 128 MB memory, scalable to 512 MB depending on the number of nodes on the network. Memory acts as Read/Write cache to boost performance.

On the other hand, an enterprise-level NAS should have minimum 1 GB memory that is expandable to 3 GB. Disk data is cached in this memory to accelerate client requests that access that data.

Network Interface: Workgroup NAS should support auto sensing 10/100 Ethernet with RJ-45 connector. Apart from the usual 10/100 Ethernet interface support, enterprise-level NAS server should support Gigabit Ethernet with both fiber/copper connectivity.

NOS: Most NAS systems should support multiple operating environments, some even allowing file sharing on the same device. For customers this means flexibility, as a cross platform NAS not only provides standardization of file services, but can also lead to cost savings in staffing, training and deployment. Compatibility list should include:

• Windows NT/2000
• All flavors of Unix/Linux
• Novell Netware
• Macintosh
• HTTP

Redundancy: There is no need for built-in redundancy in workgroup NAS, since the cost factor becomes an issue. On the other hand, enterprise-level NAS should at least provide RAID level (0/1/5) protection for disk drives which utilizes the same processor/memory for RAID operation. Since enterprise NAS are robustly designed for 99.999 percent uptime, it should provide redundancy from every prospective point like:

• Power supply (N+1)
• Fans (N+1)
• Drives (Hardware RAID with RAID 0/1/5/10) with Hot spare/ Hot swap features
• Network Interface cards (Quad10 /100 / Dual Gigabit cards)

Performance: Performance for NAS is measured in terms of Mbps. For workgroup NAS the performance should be at least in the range of 30Mbps to 75Mbps. A NAS solution which offers performance of 30Mbps can suffice the file serving needs of 25-30 nodes within a network.

Enterprise NAS performance is based on the following parameter:

• I/O performance (from 10000 I/Ops to 75000 I/Ops)
• Netbench (100 MB/sec to 160 MB/sec)
• Sequential read write performance (120 MB/sec to 200 MB/sec).
• Tape backup throughput ( 100 GB/ Hour to 200 GB/hour )

Alert system: NAS devices should have some type of alert messaging system pertaining to drive failures, drive/file system rebuilds, drives reaching capacity, unit reboot, unit overheating and backup related messages, to administrator / user in the following manner:

• LCD display on front panel
• Event log option with browser management support
• E-mail notification via SMTP
• Event notification via SNMP

Application areas

Here are some examples that might help you in deciding whether a NAS solution is appropriate for your storage needs.

Unix and NT file sharing/storage consolidation: Since NAS offers standardized, reliable and integrated file locking, it is suitable in any application where business advantage can be gained from sharing data between Unix and Windows and from consolidation of data from numerous and distributed Unix and Windows servers. For example a Windows client from purchase department can access a Unix-based electronic document system for engineering design in any engineering industry.

Technical/Analytical Application: NAS is ideal for engineering application like Geosciences where a large file or a group of files are simultaneously accessed by multiple Geoscientists to perform data analysis on large database. NAS is also well suited for decision support application like data warehousing and data mining where companies collect large amount of data for conducting statistical analyses to identify important trends.

Internet and Intranet applications: NAS devices can be used as Web attached storage/Web cache in Internet applications to offer significant improvement in system performance and content availability. Internet applications include Web hosting, e-mail, e-commerce and streaming media application.

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