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Types of NAS

Inside Guide: Making the Most of NAS for Backup
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The idea of network-attached storage is fairly self-explanatory. It’s a self-contained pool of storage resources connected to and accessible from the local network. However, as a category, NAS divides into three broad sub-markets: consumer, SMB, and enterprise.

Consumer NAS enclosures, which typically also serve the small office/home office (SOHO) market, will contain from one to six drive bays, with only one or two bays being typical of the low-end home market. Not surprisingly, expected use cycles on these devices are fairly light, with only sporadic use from a handful of systems. (The exception here is in the case of media server NAS applications, which we will soon detail in a subsequent article.) The ARM processors common among consumer NAS products may feel underpowered to some, but even the resulting curtailed performance is still sufficient to meet most home needs. Consumer and entry-level business NAS enclosures may or may not be sold with included hard drives.

The biggest problem with these lower-end NAS solutions is their lack of redundancy. With two drives, users will either mirror their drives, which provides protection but entails losing half of the paid-for capacity, or else run them striped into a single volume, which offers speed benefits as well as all of the purchased drive capacity but no on-device data protection. Either way, consumer NAS products generally lack the performance, protection, and reliability levels expected of business-class products, but they may prove quite sufficient for consumers assuming that users still back up their critical files to a secondary target, such as cloud storage. With larger file sets, such as the many gigabytes to terabytes typical of a corporation, restoring such amounts of data from the cloud can become infeasible in terms of time. This is one of the reasons that companies will invest more heavily in NAS.

At the SMB level, it’s assumed that NAS solutions will be servicing a higher number of users for a much higher percentage of the time. While a few two-drive products may purport to be suitable for SMB, four bays is the practical starting point, with six and eight bays being very common in the segment. These machines generally step up into Intel CPUs and more RAM in order to better deal with the processing load of RAID parity computation, particularly across a higher number of drives. (Parity involves calculating the data from bits on at least three drives and storing the results such that any drive in the array can be reconstructed from other array members.) Performance begins to matter at this level since businesses often make NAS drives their primary storage target for workers to help improve centralized data organization and consolidate resources. If a NAS enclosure gets bogged down with traffic generating too much processing load, then access performance will suffer, thus impacting worker efficiency and workflow.

Note that especially with six- and eight-bay SMB NAS solutions, administrators will often make at least one of the drives a “hot spare.” In the event of an active drive failure, the NAS can automatically take the failing drive offline, replace its logical position in the array with the hot spare, and begin rebuilding the failed drive’s data onto the new drive. Once a failing drive exits a RAID, the array will enter a “degraded” state noticeably slower than its normal state. Depending on the RAID configuration, a second drive failure while in degraded mode could result in complete data loss within the array. Clearly, the object of the game is to get through rebuilding and out of degraded mode as quickly as possible, and this becomes easier with hot spares present than waiting for an admin to procure a replacement drive and manually install it.

Enterprise NAS simply builds on the same concepts present in SMB NAS: more drives, more spares, more RAID options, and more performance from higher-end components very much in line with conventional server hardware. Enterprise NAS solutions will usually be rackmounted. While lower-end NAS generally rely on embedded Linux distributions and Linux logical volume management (LVM) for RAID control, higher-end SMB NAS and most enterprise NAS will feature discrete hardware-based RAID controllers. These help to offload resource-intensive storage tasks from the CPU and improve overall performance. Also, given their much higher user counts and associated bandwidth needs, enterprise NAS solutions may step up from gigabit Ethernet into 10-gigabit Ethernet (10 GbE) connectivity across multiple LAN ports.