Choosing the Right NAS Device

NAS is a dedicated, high-capacity storage device that has its own OS and software and is connected directly to the network. Since NAS devices come with several specific data-management and storage features, they eliminate the need to buy separate third-party backup software. 

There are several features to be considered when choosing a NAS, the prominent ones being 1)easy installation, 2) cross-platform file sharing, 3) data

reliability and availability, 4) security, 5) monitoring and management. File-serving performance is also

important.

Easy installation



Adding a NAS device to an existing network should be as simple as 'plug and play'. For that it should come preconfigured for file serving, which means pre-installed/configured OS, disks and other services so it's ready to work with the existing client software. The only effort required to bring it up should be plugging in the power cord, connecting the Ethernet cable, turning on the power and configuring the network interfaces. 

Cross-platform file sharing



A typical network will have different types of clients: Microsoft, Novell, Apple and UNIX/Linux. A NAS device should appear on the network as a native file server to each of its clients with files saved and retrieved in their native file formats. To achieve this, a NAS should support different network protocols.

Data reliability and availability



Single-purpose NAS appliances are more reliable than general-purpose servers designed to handle diverse tasks. The OS in a NAS device is optimized for file-system I/O and networking. NAS appliances are streamlined and highly integrated because they don't have any unnecessary components, such as a local display. A higher degree of integration enhances the NAS appliance's stability, and fewer components reduce the risk of failure. Other features that provide data reliability and availability are RAID, data replication, backup and snapshots.

RAID



For better performance and reliability of data, disk drives in a NAS device should be configured as RAID. RAID-5 is most suitable for NAS devices as it provides better disk I/O performance and fault-tolerance against single-disk failures.

CyberMedia Labs' reviewers configuring 20 client machines for stress testing the NAS devices

Data replication



Data replication keeps an up-to-date copy of critical data in a separate location, online and ready for use at any time, enabling fast disk-based recovery in case of a disaster.

Data backup



A NAS device should also support backing up of data to a local tape drive or network backup server.

Snapshots



Snapshots are incremental point-in-time copies of stored data and are created on the local devices' disks only. They allow easy restoration of data without having to access the tape. However, snapshots are not a replacement to tape-based back-ups, as there is a limitation

to the disk space that can be reserved for creating snapshots.

Security

Here, the following are important: Authentication 



A NAS device should be able to integrate with your existing network infrastructure, by central users-authentication through a directory service, such as Windows' ADS or UNIX's NIS. This also saves the administrator from defining local users on the NAS device, which will ease administration and management. 

Access control



ACLs (Access Control Lists) allow file- and share-level access for authenticated users and groups to files and folders stored on the NAS. With ACLs, only

users with requisite credentials can access files stored on the NAS.

Logging



NAS devices should audit and log most tasks done on them-log on, log off, security modification, password changes, user creation-allowing administrators to track any attempts at unauthorized access.

Anti virus



With the growing threat from worms, viruses and Trojans, NAS should ensure protection to the files stored on it. Some NAS devices let you install anti-virus software on them, whereas some let you scan stored files using an external anti-virus server, if present on the network.

Monitoring and management



Remote management and monitoring is what everybody wants in a NAS. A few features a NAS device should therefore have are -Web-based interface, remote desktop connectivity, remote login, e-mail and SNMP notifications, disk quota management, file screening and storage reports.

Web-based interface



A NAS device should let you do all monitoring and management from a Web-based interafce, which is accessible from anywhere on the network. Remote desktop connectivity and remote login through telnet or SSH, also provide ease of management.

E-mail and SNMP alerts



E-mail and/or SNMP notification of critical alerts are important for diagnosing error and fault conditions, so that administrators can take preventive measures before any major fault occurs.

Disk quota, file screening, storage reports



Disk quota lets administrators define how much storage space does every user accessing the device have. This way a single user cannot fill up the entire storage space on the device. File screening helps control which types of files are allowed on the NAS, allowing you to restrict certain types of files, say MP3, JPEGs, etc from being saved on it. Storage reports provide comprehensive information about File Type Summary, Directory Quota Usage Summary, Large Files, Files Not Being Backed Up, etc for the files stored on the NAS device.

Performance



A NAS device's performance is measured by the total file-serving throughput that it offers to users connected to it. It's measured in MBits/sec, and a higher value is better. This time, we stress tested two NAS devices using a very elaborate setup, explained below followed by the individual results. 

The purpose of a NAS device is to serve files to users. So, this is exactly what we tested the two NAS devices for. This can be done by putting a large number of user file I/O load on the NAS. The purpose is to stress the device to a level where it can't handle more user requests and the data throughput starts decreasing. Then we record the maximum data throughput achieved by the device, expressed in

Mbits/sec.

To generate the load for stressing the NAS device, we used 20 client machines, which were running the industry acclaimed NetBench benchmark clients. The NetBench clients make file read and write requests to the NAS device. A single NetBench client generally stresses the NAS as much as many actual users do, so you can run test suites with a relatively small number of clients and still get an accurate measure of your NAS device's performance. To accurately represent the interaction clients have with the server, NetBench is modeled after a real file-server environment. By this we mean an environment where your application, such as a word-processing or spreadsheet program, is running on the client, and the client is primarily using the server to access data. As a result, the server's disk I/O speed and the network I/O speed are major areas that affect test score.

There's a NetBench Controller, which directs the clients to start and stop generating file I/O requests to the NAS device. At the end of each test, it calculates the throughput score by accumulating individual results from the clients.

The 20 client machines were split into two groups of 10 machiens and connected to two different switches. Most NAS devices come with two network interfaces, so one network interface was connected to one switch and the other to the other switch. By connecting the clients to two separate network segments, the chances of data traffic bottleneck within the switch are also eliminated. Further, the NAS devices were connected to the high-speed gigabit-Ethernet ports on the two switches.