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NAS Class

The next key fork in the decision road is whether to choose a single drive or multi-drive RAID product. In our NAS Charts, Ranker and Finder, we refer to this as class. Fortunately, NASes divide into three classes: No RAID; RAID 1; or RAID 5. Another way to put this is: single drive; dual drive; or four drive and higher models.

The RAID vs. No-RAID decision is not about data security! It's primarily about how much capacity you want in a single physical box.

You should never trust your precious data to a single device, no matter what RAID level (0, 1, 5, 6, 10, etc.).

RAID is not backup!

RAID was created to enable the construction of large storage arrays out of relatively inexpensive hard drives, using redundancy to compensate for the relatively short life of hard drives. RAID 5 and 10 arrays should be able to withstand the loss of a single drive without losing your data and RAID 6 should be able to lose two drives. But no RAID array will guarantee against data loss if the power supply or controller board fails, or the unit is physically damaged or stolen.

Consider not using RAID if your storage needs can be satisfied with a single drive (currently at 6 TB!). If you need more storage, you can always add another NAS and probably still come out ahead for cost.

Note!NOTE:While you might be tempted to think you can push the single-drive crossover point by attaching an external USB drive... don't!

External USB-based storage is usually treated as a separate share that can't be combined with internal storage. Read / write speeds are slower and you usually have to use a non-Windows readable format on the drive (XFS, ext3/4) for optimum performance.

The main reason to choose a RAID 1 NAS over a No RAID is if you like the added peace of mind provided by RAID 1's continuous data replication. RAID1 also speeds recovery time when a drive evenually dies. All you need to do is replace the failed drive and start the rebuild process. Your data remains online during rebuild.

When a No RAID NAS dies, you'll need to restore the data manually from an attached drive, network share or rsync backup. This will be slower, since these methods have lower bandwidth than an internal drive-to-drive copy.

The main reasons to choose a RAID 5 NAS are if your capacity requirements are over 6 TB, your storage capacity growth rate will put you over that level sometime in the next few years or you need the absolute highest performance for multi-user applications. The most powerful hardware platforms, including 10GbE support, are available only in RAID 5 class NASes.


It might seem strange seeing this topic so far into the article, since some NAS buyers place performance above almost all other criteria. But many NAS shoppers agonize over the choice, when in fact, other factors can make it less important.

The key performance criteria for NASes are read and write throughput. Throughput is affected by four things: NAS performance; Client performance; Network performance; and what you are reading and writing.

The last factor is illustrated by the Benchmark Summary below. The [NASPT] File Copy benchmarks use a single large sequential data file (1.15 GB windows .BAK) that will show a NAS' highest transfer rate. In contrast, the [NASPT] Directory Copy benchmarks move 2,833 files in 44 folders and, in this case, show one tenth the throughput of the File Copy benchmark.

NAS Benchmark summary example

NAS Benchmark summary example

File size aside, NAS Performance is primarily determined by processor platform, then internal OS and filesystem used. What generally doesn't matter is the performance of the hard drive used. Hard drive access time, seek time, etc. are generally masked by the overhead of moving data across a network.

NAS RAM size helps only if the file size being read or written is smaller than the RAM size. So if you copy a lot of 1 GB ripped DVD VOB files, then you'll want a NAS with at least that much RAM. But generally, unless you are frequently writing and reading a lot of small files, RAM size won't matter much.

Client Performance is influenced by the same factors that affect NAS performance, i.e. processor, RAM and OS. Newer OSes like Windows 7 and 8 include optimizations that can significantly improve network throughput when transferring large sequential files (think music and video). Gigabit Ethernet adapters also matter; some can boost throughput by 100 - 200 Mbps.

Network speed also must be fast enough to not be a bottleneck. For most of today's NASes, that means a Gigabit Ethernet connection. Even inexpensive single-drive NASes (and some routers with USB storage features) exceed the 12.5 MB/s limit of a 100 Mbps Ethernet connection. If the client or network connection is slower than the NAS, then you won't be able to get full benefit from a very high-performance NAS.

If you're using a wireless connection, you probably won't be able to take full advantage of even low-end NAS 50 MB/s transfer rates, even if using an 802.11ac router. You can only take advantage of 802.11ac's Gigabit link rates if your wireless devices also support them and most don't. You also need very strong signal levels to achieve top throughput. Bottom line is if you're buying even a mid-range NAS, you'll need Gigabit Ethernet to take full advantage of its performance.

If the NAS you're considering has File Copy throughput over 100 MB/s, it is likely bumping up against the limits of a single Gigabit Ethernet connection (125 MB/s). But additional Gigabit Ethernet ports available on these higher-end NASes won't help remove this bottleneck for single client use. Port aggregation helps only to widen the "pipe" to the NAS for multiple clients. (Read this brief presentation for a nice and clear explanation.) If you want the fastest way to move large sequential files for individual users, you'll need to move up to 10GbE. Check out our Confessions Of A 10 GbE Network Newbie series to help start your transition.

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