How to Choose and Benchmark a NAS

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Sunday, February 04, 2007

Key factors when buying!!!

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Besides performance, you also need to look into the features offered by the NAS before buying. If you think a NAS is nothing but a set of disks connected together to offer storage space on the network, then think again. You're in for a surprise. We found lots of small but crucial points that you need to look into when scouting for a NAS.

Expandability
Two key elements that can be expanded are hard drives and RAM. Not all vendors allow you to upgrade RAM in their boxes. Their claim is that their NAS boxes are optimized and tuned to work with the RAM they ship with. If you need a RAM upgrade, then the only option is to upgrade to a new box with more RAM. So besides spending time configuring the new NAS box to work on your network, you'll also be busy migrating all data from the old box to new one. Do check with your vendor on RAM upgradability before buying.

Hard drive upgrades are another story altogether. Many vendors don't allow you to just pick up a hard drive from the market and plug it into a free bay in your NAS. The reason for this is that every hard drive has its own firmware version, and the NAS vendor certifies hard drive models to work with its NAS. If you plug in a hard drive with a different firmware version into your NAS box, even if it's the same HDD brand, then the NAS box's warranty gets void. So what happens if one of the hard drives in your NAS box crashes? You can't plug in any hard drive you want in it. So either you buy a spare hard drive at the time of purchasing the NAS, or shell out extra money to pay the NAS vendor for a replacement. Needless to say that the amount you have to pay is directly proportional to how quickly you need the replacement!

This also opens up another interesting aspect. If you want to add a new hard drive to increase the capacity of your NAS box, then many vendors will charge you extra for it. The licensing models of some vendors are based on the capacity they provide you.

Available storage
Here's another gem to worry about. Did you know that a 1 TB NAS box will never give you 1 TB of storage space, because a part of it is used up by the RAID and the OS? Even if you did, then you may not know that there can be major variations in how much storage space is used up by them. So a 1 TB NAS box could have anywhere from 600 to 700 GB of available storage space. That's a whopping 100 GB difference in available storage space! To give you an idea, consider a NAS box that has 250 GB x 4 disks, which amounts to 1 TB storage capacity. When you configure it in RAID 5, then one disk is gone, reducing the total available storage capacity to 750 GB. Further, the vendor may use more space to host the NAS OS, take snapshots for OS recovery, etc. This could easily take anywhere from 50 to 100 GB, leaving you with 650 to 700 GB of data storage space. Moral of the story: If you need 1 TB of storage capacity, then go for a 1.5 TB NAS.

Data compression
Check whether a NAS box supports compression, as it will help you utilize the storage capacity more effectively. Data in every organization increases by leaps and bounds. So you might feel that you've bought a whopping 1 TB of storage capacity for your network now, but one year later, you'll be wondering where all that storage space went. At that point, you'll wish your NAS box supported compression. Some NAS boxes we received for evaluation were running propriety NAS OS and didn't support data compression. However NAS boxes running Windows Storage server had this feature. Performance wise also it gives you negligible difference over file storing without compression.

Monitoring and mgmt
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 through telnet or SSH, e-mail and SNMP notifications, disk quota management, file screening and storage reports. You could also look out for a LCD screen on the NAS itself. This can be pretty useful in giving you lots of critical information about the NAS device and letting you control it.

File Systems Supported
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.

Data backup
Most NAS devices support backing up data to a local tape drive or network backup server. Apart from this, also look for the following:

Snapshots: Incremental point-in-time copies of stored data are created on local devices' disks only. They allow easy data restoration without having to access the tape. 

Disk Backup: Some NAS boxes come with a disk backup option, where backup is done on NAS storage only. For this you have to configure the RAID in such a way that at least one disk should remain free. For example if you have four drives, then create RAID with three drives and leave one for disk basedbackup.

Data replication: To keep an updated copy of critical data in a separate location, online and ready for use at any time, thereby enabling faster DR.
Device to device replication: Two NAS box are connected in parallel and synced for high storage availability. Check whether your NAS also supports automatic failover to the stand by NAS. 

Backup to DVD: Another type of backup that some vendors provide. It's useful when you need to send out some very critical data.

Security
A NAS device should easily be able to integrate with your existing directory service for authentication. Anti virus: How does your NAS vendor support anti-virus software? Some NAS devices allow you to install anti-virus software directly on them, while others let you do remote scanning from an anti-virus server on the network.

Access Control Lists: Allow file and share-level access for authenticated users and groups to files and folders stored on the NAS. Check what kind of ACL is supported by the NAS.

Logging: A good NAS box should audit and log most tasks done like log on, log off, security modification, password changes, user creation, etc
E-mail and SNMP alerts: These are a given, and a concern if some vendor doesn't provide them.

Storage Control
It's criticla to prevents a user from filling up the entire storage space. Check for file screening support to control which types of files are allowed to be saved on the NAS. How comprehensive are a NAS's storage reports?

High availability
Today even an entry level NAS comes with dual NICs. Check whether it's able to do network load balancing, automatic failover, and teaming. The last option aggregates the two physical links, thereby doubling link speed.

Other features to check
A NAS box that can support databases is different from one that supports basic file storage, and their cost differential is also
significant. You can also look for a redundant power supply in the NAS.

Price
Last but not the least is the price you pay. There's a huge variation in the prices between various NAS boxes.

It all depends upon how many features is the vendor bundling into the NAS. For instance, the HP NAS we received cost Rs. 3.15 Lakhs. It gave only 629.9 GB storage space, but also had tons of useful features. The Level One NAS on the other hand, was priced at only Rs. 98,500, gave storage space of 1.3 TB, but its features were limited.

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