Buyer's Handbook: How to buy NAS systems for any organization Article 3 of 6

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9 enterprise NAS features and purchase considerations

If you're in the market for enterprise NAS, pay close attention to the system's form factor, the media it supports and how easy it is to increase capacity, among other features.

Enterprise-scale organizations often use SANs, but NAS still has its place. Here are the nine important features an organization considering an enterprise NAS purchase should review first.

1. Form factor. It's often assumed that an enterprise-grade appliance will be rack-mounted, but some are designed to sit on a shelf. If the organization is considering a rack-mounted NAS appliance, it will need to determine how much space it's willing to sacrifice. A 4U appliance will take up more rack space than a 2U appliance, but it also will provide more raw storage capacity.

2. Media appliance supports. Although it is becoming less common, some vendors force customers to buy disks from the appliance manufacturer.

Companies in the market for a NAS appliance should also verify that the appliance conforms to modern standards. Hardware vendor websites will sometimes offer a seemingly great deal on an appliance without disclosing that it's an older model.

Potential customers also should check the appliance's maximum throughput and overall capacity, as some enterprise NAS appliances do not support high-capacity disks. Similarly, an appliance might have a maximum overall capacity that is less than the aggregate capacity of the potentially installed disks. An appliance that has 12 drive bays and supports 4 TB disks should theoretically provide up to 48 TB of storage, but it may have a maximum overall capacity of 32 TB. In such a configuration, the four remaining disks may be reserved for use as hot spares.

3. Ease of increasing the appliance's capacity. Suppose a company has an appliance with 12 drive bays, and it uses only eight of them, but now needs to add few extra disks. What happens when it installs those disks?

Some appliances require IT 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 the backup. This process is tedious and time-consuming.

Ideally, an enterprise NAS appliance should include a feature to automatically restructure the existing RAID array when capacity is added. IT staff shouldn't have to delete volumes and rebuild array sets simply because they've added extra disks to the appliance. The appliance should be smart enough to use those disks without manually reconstructing the RAID set. Similarly, if an existing disk is replaced with a larger capacity disk, the appliance should be able to use the new disk without requiring IT 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 staff to mount the drive into a special caddy prior to placing it in the appliance. Similarly, there are appliances that require the use of special vendor proprietary tools to install hard drives. While the need for such a tool might seem trivial, consider the implications of having to replace a failed drive and not being able to locate the required tool.

4. Support for storage tiering. Storage tiering refers to the ability of the appliance to use SSDs as a cache for frequently accessed data. Tiering is gradually giving way to the use of all-flash arrays, but it remains an important consideration for appliances using spinning disks.

Ideally, developers should automate the storage tiering feature. That enables the appliance to differentiate between rotational media and solid-state media, and use the solid-state media as a cache with no further instructions. The administrator shouldn't 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.

5. Network bandwidth. Bandwidth is the limiting factor when it comes to enterprise NAS appliance performance. As such, companies must ensure their appliance contains as many network adapters as possible. It's also a good idea to verify what speeds are supported. Most enterprise NAS appliances support gigabit Ethernet, but companies may find support for speeds of 10 Gb or higher.

6. Hardware redundancy. This is a major consideration when it comes to enterprise NAS appliances. Some appliances offer redundant cooling and power supplies. Similarly, there are appliances that let companies designate HDDs and network adapters as hot spares that can dynamically take over in the event of a hardware failure. Developers design hardware redundancy to protect against a component-level failure.

7. Replication. Occasionally, a hardware failure may compromise the entire appliance. When this happens, IT teams must have a plan that enables them to continue to operate in spite of the failure.

Appliance-level storage replication is one way to do this. Some appliances will allow an organization 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 data center.

8. Data storage features. An enterprise NAS appliance should have a duplication engine that can eliminate redundant data and help limit physical storage consumption.

The appliance should also support storage-level encryption to ensure data can't be retrieved from a stolen drive.

9. 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 buy multiple appliances. In these situations, organizations don't want to manage each enterprise NAS appliance individually. The vendor should offer a management portal that lets the customer gauge the health of all the appliances at a glance. Ideally, companies could use such a portal for simultaneously configuring multiple appliances.

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