Hard disk and NAS have been an inseparable duo for years. Yet this golden combination of storage space and smart usage options is under pressure, because after the notebook and desktop PC, the SSD is also on the rise in the NAS. Let’s take a look at the pros and cons of a NAS full of SSDs instead of hard drives.
A NAS is almost always bought empty and then filled with one or more hard drives for storage. Because a NAS quickly contains several disks that are under heavy load and part of the storage capacity is lost when using RAID, choosing the right disks is not an easy task.
The choice is usually mainly determined by the storage capacity (preferably as large as possible) and the price (preferably as low as possible) and to a much lesser extent by the brand and whether they are special NAS drives. And although there are still considerable differences between the hard disk and the solid state drive (ssd) in terms of storage capacity and price, the latter is also increasingly emerging as a replacement for the hard disk.
The SSD owes its success to the use of memory chips for the storage of data. The traditional hard disk uses several rapidly rotating disks with a magnetic top layer, above which a read and write head moves quickly back and forth. The moving parts mean that the hard drive produces a lot of heat and noise, and above all is less energy-efficient and vulnerable.
All things that do not speak in favor of the hard disk, especially when it has to perform under heavy load for a long time and reliably, such as in a NAS.
Favorite choice
However, the hard disk when filling the NAS still the favorite choice of many. The biggest argument here is undoubtedly the storage capacity. The latest hard drives offer 18 TB of storage and it is only a matter of months until the first 20 TB of storage capacity is available. These are capabilities that no SSD even comes close to. With the SSD, 1 TB or 2 TB is still the upper limit. And even though there are models with 4 and even 8 TB, they are certainly not yet common, partly due to their price.
A second advantage of the hard disk is precisely that price, although the prices of hard disks have been stable for several years. The top models are also affordable and offer more storage capacity year after year. For the NAS buyer who opts for hard drives, this means that they either need fewer and fewer drives to build the storage capacity they want or get more and more storage capacity for the same money.
Another important advantage of the hard drive is its reliability. Despite the heat production and the moving parts, the reliability of the hard disk is unprecedented. The cloud storage and backup specialist Blackblaze annually publishes the failure rates of the now more than 165,000 hard drives that the company uses for its services. And despite the continuous and high stress these drives undergo, less than one percent of them fail annually.
In fact, in 2020, the 6TB Seagate ST6000DX000 performed best with an Annualized Failure Rate (AFR) of just 0.23 percent. And then that is also a desktop model hard drive. NAS buyers who want even more security and longer life can also opt for dedicated NAS drives such as the WD RED, the Seagate IronWolf and the Toshiba N300 series.
Advantages of SSD also for NAS?
An SSD is smaller than a hard disk, faster, quieter, consumes less power, has no moving parts, produces less heat and is not sensitive to vibrations and magnetic fields.
Because SSDs have no moving parts, they offer speeds well above those of a typical hard drive. Also, fragmentation is not an issue, files can be written anywhere with little impact on read or write time, resulting in read times much faster than any hard drive.
Not all of these benefits are equally important for use in a NAS, but they are certainly attractive. Attempts by, for example, Synology and especially QNAP to give the NAS a place in the living room, for example, always failed due to the size of the device and especially the noise of the fan, needed to dissipate the heat from the hard disk.
A NAS with SSDs might make it possible. The belief among NAS manufacturers that a location closer to TV and media installation would benefit usage was and probably still is.
It is clear that the SSD also has advantages over the hard disk, but when used in a NAS, these are not all equally important. A direct comparison of both strengths and weaknesses therefore does not immediately lead to a clear result.
For example, a hard drive is much more vulnerable than an SSD that has no moving parts at all due to the use of revolving plates with a moving read and write head, but once installed, the NAS housing is usually a very stable and safe environment, also for a hard drive. The chance that it will fail due to physical shock is very small, while the risk of resonance of several disks in an enclosure, mentioned by the manufacturers, mainly occurs at really large volumes of many disks.
And also in terms of reliability, the advantage of the SSD is less, because in a NAS usually several disks are placed in a RAID configuration. Together they then form one storage volume, where – if RAID 1 or higher is chosen – the stored data is protected against loss due to a hardware failure. If a disk fails, no data is lost.
RAID with hard drive and ssd
RAID combines multiple storage media into one logical storage unit. The goal may be to increase speed, but when used in a NAS, increasing capacity and reliability is more often the reason.
Usually hard disks are used in a RAID configuration, but it is also possible to do this with SSDs. Only then is the relatively high price of the SSD and the much smaller storage capacity in comparison with hard disks even more revengeful.
With RAID, part of the storage capacity of the disks or SSDs is used to provide extra speed or reliability. With RAID 1, the technique for RAID with two disks, that is even half the storage capacity, with RAID 5, which is common with four disks, a quarter.
With today’s largest hard drives, this provides secure storage of 18 and 54 TB respectively, both more than adequate for most applications. If you do the same with the largest SSDs, then the 8 TB with RAID 1 will certainly be insufficient. The 24 TB that remains with RAID 5 with four SSDs is then better, but at a much higher price.
If you apply a budget limit of 500 euros for hard drives and SSDs, you can create a capacity of 10 TB with two WD Ultrastars of 10 TB each, while two WD RED SA500 SSDs of 2 TB each provide only 2 TB storage capacity. In RAID 5, four WD RED NAS hard drives of 4 TB each provide 12 TB of storage, while four Samsung 860 EVO SSDs of 1 TB each provide only 3 TB.
Network point as bottleneck
A plus of the SSD is the speed with which the data can be written and read. A hard disk usually achieves between 50 and 150 MB/s, a SATA-ssd effortlessly reaches 500 MB/s. But when used in a NAS, SSDs rarely deliver a different user experience. This is due to the speed of the network.
Most networks are gigabit networks and so are the network ports on most NAS devices. Even a NAS with only hard drives often manages to use the network port almost completely. To use the higher speed of SSDs in a NAS, you need either a NAS with multiple gigabit network ports that can be merged into one faster connection, or a NAS with a 2.5 or 10 Gbit/s network port that connects to a switch with the same quality is linked.
Certainly the latter, a really faster network than gigabit, only occurs in business environments. NAS devices with at least one 2.5 or 10 Gbit/s network port are still scarce, but the supply is increasing. QNAP and Asustor provide their NAS models for the more serious consumer and use in small office environments with a 2.5Gbit/s network port almost standard and are forcing Synology to follow suit. Many more luxurious PC motherboards are now equipped with a 2.5 Gbit/s network connection.
Opportunities for the SSD
If you read the above, you will quickly think that it will take a while before the SSD has a real chance as a replacement for the hard drive in the NAS. Nevertheless, there are certainly opportunities for the ssd, although for the time being it is not yet a one-for-one replacement for the hard disk.
The latter remains in most NAS configurations to create really large storage volumes, but the SSD gets an important role next to it. For example, by creating multiple storage pools in one NAS, one for the hard drives and one for the SSDs, and using each for the type of storage and functionality that fits the underlying storage technique.
Although the speed of the SSDs is not yet very usable in the network, it is superior to that of the hard disks for all processing in the NAS. Use of this speed and the internal processing of the data are noticeable when using virtual machines on the NAS or large data processing operations such as databases on the NAS. The condition is that the NAS itself has sufficient memory and a good processor. If these do not suffice, a new weakest link has already been found.
Combining hard drives and SSDs in a NAS is also easier when the NAS offers space for multiple drives or SSDs. Until now, two disks were the lower limit and with four disks you had a large NAS. But to create two RAID5 storage pools side by side, six disk bays in the NAS are needed. That’s probably two and possibly four more than most NAS devices consumers have bought in recent years.
SSD as cache
You can use SSDs in the NAS not only as a direct storage medium, but also as an SSD cache. It uses the speed of one or more SSDs to improve the read and write performance of a volume on the NAS. The cache can consist of one or more regular SATA SSDs, but M.2 SSDs are also an option. This all depends on the NAS model.
Not every NAS supports SSD caching and not every NAS that supports SSD caching also offers the option to use M.2 SSDs. The latter are preferable for this functionality, because an M.2 SSD achieves up to five times faster read and write speed than a SATA SSD.
If the NAS does not directly support the installation of M.2 SSDs, some models offer the possibility to add this support with an expansion card. Sometimes a 2.5Gbit/s port or even faster network interface is placed on that card, making it an even more valuable upgrade.
But there are also drawbacks. The disadvantage of the limited rewritability of the NAND memory chips is particularly apparent with SSD caching. With intensive use, the SSDs can be worn out after one or two years and need to be replaced.
It also quickly requires a significant investment of several SSDs and sometimes an expansion card, and that only to speed up existing storage. Conversely, it can also be a sound investment, precisely to extend the life of previously purchased drives and NAS hardware.
Shared future
In laptops and desktop PCs, the hard drive has been almost completely displaced by the SSD, but in NAS that is not yet the case. There are still too many disadvantages to the SSD for that. Compared to the hard disk, especially the storage capacity is still too small and the price too high. Certainly with a device such as a NAS, where storage capacity is so important, the hard drive will therefore remain the first choice for a while.
Until the time when one or a few SSDs offer sufficient storage capacity for the average user, the SSD can perfectly fulfill a role next to the hard disk. Most opportunities lie in more specialized scenarios such as virtualization and large data volumes. If you now only have hard drives in your NAS, you don’t have to worry yet.
.