When choosing a hard drive for NAS, they recommend taking into consideration these main factors: the size, the maximum possible number of NAS HDD in RAID, disk reliability in respect to potential workload, the security level and the noise level.
Among other things, the choice of NAS drives will be determined by functional tasks they will be used for. For instance, a disk array can be used as storage for databases, a file server, a web server, a workstation, which, in their turn, can be geared towards video recording, image editing, game center, and etc.
Since disk reliability and performance requirements must be determined by the alleged workload of the system at the current moment and in prospective, it is necessary to consider the potential scenario of how it will be used. With typical workload, for example, recording TV shows and playing them back, the scenario is more consistent and predictable. With irregular workload, when the data is recorded and read from the disk randomly, the scenario becomes more intense and unpredictable, which influences reliability of its performance. Reliability can also be affected by the disk interface.
To ensure the necessary level of security, some disks use self-encryption and instant secure wipe-out. Such HDDs are necessary for corporate use, for companies that store large amounts of information intended for limited use.
For home NAS modules an important parameter is the noise level produced by the disk array during its operation, especially if the drive is located in the room where people sleep. Experts recommend choosing hard drives with low noise level upon access and with minimal heat level during the operation. The NAS cooling system in this case will work much quieter. In linear operations the main noise of the NAS is produced by the cooler. Modern discs on hydrobearings do not make noise upon linear reading. But if disk operations are, mainly, “random” (random, chaotic, erratic), there is nothing to complain about – you can configure, for example, a caching system to speed up access to data in the torrent tracker.
Except for the size and the price, the specific parameters of hard drive for NAS, according to PrizedReviews.com, are the following:
Each NAS HDD consists of several magnetic plates for recording data of different sizes – from 400 GB to 2 TB each. The larger the size of the hard disk plates, the higher the recording density. High recording density accelerates the disk speed, the response time, if the script is, for example, consists of streaming videos, that is, sequential reading/recording. If the DM application scenario involves random reading/recording, the recording density will no longer be as important. However, with greater density, reading/recording heads will have to move to a smaller number of tracks behind new data. That is why there is such a definition as Locality, i.e. proximity of location of data.
Spindle Rotation Speed
High-speed disks for NAS arrays are the devices with a spindle rotation speed of 7200 rotations/min. In combination with high recording density, these NAS drives show excellent performance. High speed of rotation compensates for a low recording density (the recording density is determined by the capability of the electronics’ reading/recording channel and, indeed, depends on the speed of the spindle’s rotation. But we cannot talk about “low” density because everything is determined by the data volume that we can record/read per rotation. A fast spindle provides shorter response time to random requests, while the linear speed depends only on the number of sectors on the track and the spindle rotation time).
It can be increased by special technological solutions, for example, 2-drive system of positioning of the heads. A two-drive positioning system was intended to increase positioning accuracy upon increase in recording density. The tracks were becoming so thin that the old “yoke” of the head unit could not stay precisely on the track. And since the reading/recording speed accelerates with the increase of recording density, more sectors can be counted per rotation of the plate; upon acceleration of speed of rotation of the plates, it reads the same number of sectors, but in less time.
However, according to test results, the speed depends, mainly, on the bandwidth of the NAS module network card. In addition, in home environment, in order to experience the beauty of high-capacity disk array, high-speed communication channels are required. At the same time, IEEE 802.11ac and Gigabit Ethernet are not capable of providing it at the proper level; it requires, for example, a direct connection via Thunderbolt or a 10-GB Ethernet in the entire local network, which is quite expensive for home use.
On the one hand, high performance of the disks almost always “keeps up” with high power consumption. But low energy consumption leads to: lower heat generation (up to 2 C per disk), less intensive work of the coolers, lower noise level, lower energy consumption throughout the NAS system (up to 20 kWh per year per disk). As strange as it may sound, efficiency of NAS disks is more important than their performance (with some rare exceptions).
Consider compatibility of the selected HDDs with the NAS module where they will be installed. The compatibility factor may express itself in lack of support of specific functions of the drive by the NAS system, such as the standard “sleep” mode and many other functions. Compatibility must also be maintained between the HDD NAS. For example, the type of management of the RAID 1 involves recording data to a pair (pairs) of disks) at a time, and upon using drives with different speeds of spindle rotation within the same section, a faster NAS disk will constantly wait for its slower “brother” to finish its task. However, only with “recording” on RAID1 we are limited by the speed of the slower disk, but most of the operations, according to the statistics, are “reading”. Of course, this configuration can also take place, but it is highly undesirable because in this case the RAID will lose its advantages.
We should pay attention to the original size of the disks, because if we need to replace them, we can face some difficulties, including a temporary backup of all the available data intended for moving. In terms of the price, in almost any case, the worthiest of one gigabyte (but not the cheapest one) is the disk of the largest size. But installation of such disks is not always optimal. The larger the size of the RAID, the longer it will recover upon disk replacement or after a potential failure (sometimes it can last for more than 24 hours).