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Enterprise-scale organizations often use SANs, but NAS still has its place. If your organization is considering an enterprise NAS purchase, here are the important features you should review first.
Form factor. It's easy to assume an enterprise-grade appliance will be rack-mounted, but some are designed to sit on a shelf. If you are considering a rack-mounted NAS appliance, you will need to determine how much space you are willing to sacrifice. A 4U appliance will take up more space in your rack than a 2U appliance, but will provide a higher raw storage capacity.
Media supported by the appliance. Although it is becoming less common, some vendors use proprietary connectors that force customers to purchase disks from the appliance manufacturer.
You should verify the disks supported because hardware vendor websites will sometimes offer a seemingly great deal on an appliance without disclosing that it is an older model. For example, I recently saw an ad for an enterprise NAS appliance that supported long-obsolete SATA 2 disks, but not SATA 3.
You also need to check disk speed, maximum disk capacity and the appliance's overall capacity as some enterprise NAS appliances do not support high-capacity disks. For instance, some manufacturers support only 1 TB drives even though higher capacity drives are available. Similarly, an appliance might have a maximum overall capacity that is less than the aggregate capacity of the disks that could be installed. An appliance that has 12 drive bays and supports 1 TB disks should theoretically provide up to 12 TB of storage, but may have a maximum overall capacity of 8 TB.
Ease of increasing the appliance's capacity. Suppose you have an appliance with eight drive bays, use only four of them but now need to add few extra disks. What happens when you install those disks?
Some appliances require you to perform a full backup, delete any existing volumes, destroy the existing RAID structure, create a new RAID array using all the disks installed in the appliance, create new volumes and restore your backup. This process is tedious and tends to be extremely time-consuming.
Ideally, an enterprise NAS appliance should include a feature to automatically restructure the existing RAID array when you add capacity to the appliance. You should not have to delete volumes and rebuild array sets simply because you have added extra disks to the appliance. The appliance should be smart enough to use those disks without the RAID set having to be manually reconstructed. Similarly, if you replace an existing disk with a larger capacity disk, the appliance should be able to use the new disk without you having to manually rebuild the RAID array.
Most enterprise NAS appliances support hot-swappable drives, but some appliances make it easier than others to replace a drive. For instance, an appliance may require you to mount the drive into a special caddy prior to placing the drive in the appliance. Similarly, there are appliances that require the use of special tools to install hard drives.
Support for storage tiering. Storage tiering refers to the ability of the appliance to use solid-state drives as a cache for frequently accessed data.
Ideally, the storage tiering feature should be automated. The appliance should be able to differentiate between rotational media and solid-state media, and use the solid-state media as a cache without being told to do so. Furthermore, the administrator should not have to tell the appliance which data to cache. The appliance should also recognize the most frequently accessed data and move it to the cache on an as-needed basis. As the demand for the data changes over time, the appliance should dynamically move aging data out of the cache and replace it with fresh, more frequently accessed data.
Network bandwidth. Bandwidth is the limiting factor when it comes to enterprise NAS appliance performance. As such, you should ensure your appliance contains as many network adapters as possible. It's also a good idea to verify what speeds are supported. Most enterprise NAS appliances on the market support Gigabit Ethernet, but you may find support for 10-Gigabit Ethernet. There are also some vendors that only provide 100-Megabit Ethernet.
Hardware redundancy. This is a major consideration when it comes to enterprise NAS appliances. Some appliances on the market offer redundant cooling and power supplies. Similarly, there are appliances that let you designate hard disks and network adapters as hot spares that can dynamically take over in the event of a hardware failure. Hardware redundancy is designed to protect against a component-level failure.
Replication. Occasionally, a hardware failure may compromise the entire appliance. When this happens, you need a plan that allows you to continue to operate in spite of the failure.
One way of accomplishing this is through appliance-level replication. Some appliances will allow you to replicate all the data to a secondary appliance on an ongoing basis. Depending on the type of connectivity used in the replication process, it may even be possible to replicate data to a secondary datacenter.
Data storage features. An enterprise NAS appliance should have a deduplication engine that can help limit physical storage consumption by eliminating redundant data.
The appliance should also support storage-level encryption to ensure data cannot be retrieved from a stolen drive.
Manageability. Enterprise-class organizations need storage offerings that are highly scalable. Although a NAS appliance has a limit as to how much data it can store, it is common for large organizations to purchase multiple appliances. In these types of situations, you don't want to manage each enterprise NAS appliance individually. An appliance vendor should offer a management portal that allows you to collectively gauge the health of your appliances at a glance. Ideally, such a portal could be used for simultaneously configuring multiple appliances.
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