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The drives you put in your NAS are in some ways more important than the enclosure itself, the worst case with buying an underpowered enclosure is you can't watch your Plex content on your mobile. Use the wrong hard drive and your entire collection of photos, videos or music is potentially lost forever.

Hard-drives fail

The the universal truth of file storage is that your drive will eventually expire. Opt for solid state and it's limited by its flash cycles, opt for mechanical and either from overwork or physical damage you drive will be rendered unusable. This is why robust NAS drives and storage solutions leverage RAID (Redundant Array of Inexpensive Disks) to prevent data loss. Storage is literally fragmented across multiple disks, ensuring that if a sing drive dies it can be replaced without loss of data.

Types of hard drive

A hard drive is used to write data to, read data from and store data long term, each use case will have a different set of demands however. Consequently harddrives are built with different purposes in mind. A PC may use a faster flash drive to load its operating system, and a second slower drive to store less frequently accessed data. A video security system will conversely require a drive that can be written to almost constantly. A Plex server needs drives that can be written to infrequently, but read from more regularly. A USB drive isn't likely to spend its life being hooked up to a server constantly subject to read and write cycles.

The result is different grading of drives:

External Storage / PC drives

As a rule these drives are the cheapest, expected to be accessed only as often as needed and rated to run no more than 7 hours a day. These drives will absolutely work in a NAS but are prone to overheating and generally live short lives if pressed into frequent use.

NAS drives

As the name suggests this class of drives is designed to be run 24/7 365 days a year. The disks usually rotate at a gentle 5400 revolutions per minute though faster drives also exist. This ensures less noise, vibrations, power consumption and heat. In addition, manufacturers usually give a longer warranty period on NAS disks. The emphasis for NAS drives is on read cycles over write cycles.

Surveillance drives

In contrast to NAS specialist drives Surveillance drives emphasis continual writing rather than constant reading, and as such will work but are NOT recommended for use in NAS solutions.

Flash drives

As used on USB drives these are smaller, faster, have significant capacity, and are durable due to a lack of moving parts. In spite of this these drives are generally useful for no more than 10 years of storage. However SSD drives in the NAS make little sense. You reduce the noise level and power consumption. With the usual transfer rates in GBit Ethernet of 50 to 70 MB/s, SSDs do not, however, show their speed advantage. In addition, they are still far too expensive for the capacities you want in a NAS system.

Advantages of RAID

In redundant raid networks (i.e. at least raid level 1), many NAS disks have improved functions for dealing with bad sectors. This prevents a disk from being completely removed from the group prematurely due to a read error. Seagatecalls this function ERC (Error Recovery Control), at Western Digital it is called TLER (Time Limited Error Recovery). In any case, you are on the safe side if you use disks that are listed by the respective NAS manufacturer in the compatibility list on the website.