Installing solid state drives (SSDs) into NAS appliances is such a common practice that admins may not give it much thought. That's a mistake, because there are some key considerations that can create efficiencies and cut costs when installing SSDs into your NAS storage devices.
Hardware Compatibility Considerations
Regardless of the make and model of your NAS appliances, you will need to consult the manufacturer’s hardware compatibility list before attempting to install SSDs. Many NAS vendors support only specific SSD models, or SSDs from certain manufacturers.
In some cases, you might be able to get away with using an unsupported SSD, although it is never a good idea to operate a production environment in an unsupported configuration. In other situations, the use of an unsupported SSD may fail. Some NAS vendors have designed their firmware to detect and prevent the use of unsupported disks.
As you examine the hardware compatibility list for your NAS appliance, it is important to be mindful of storage capacity. Some, but not all, NAS vendors specify both a minimum and a maximum supported SSD capacity. Using SSDs that fall outside of this capacity range can deliver unpredictable results.
How Will the SSDs Be Used?
The No. 1 consideration that you will have to think about is how the SSDs will be used. In other words, are you planning to use the SSDs for the direct storage of data, or are you planning to create a high-speed tier that uses SSDs for caching purposes? In either case, there are some essential considerations.
For example, you will need to consider whether the slots where you intend to install your SSDs are dedicated to a specific purpose. Let me show you an example.
The screen capture shown in Figure 1 shows the management interface for a QNAP NAS appliance. This particular screen lists the disks that are installed in the appliance. In this case, there are four SSDs (labeled SSD 1 through SSD 4) and 12 HDDs (labeled Disk 1 through Disk 12). The first 11 HHDs are being used for data storage, and Disk 12 has been designated as a hot spare. At the bottom of the list of disks, you will see the listing for two empty drive bays, labeled M.2 SSD 1 and M.2 SSD 2.
This NAS appliance has 12 HDD bays and 6 SSD bays.
The M.2 slots are designed to accommodate PCI cards, each of which contain one or more NVMe storage devices. n the case of my NAS appliances, storage devices that are mounted in the M.2 slots can be used only for caching (or performance tiering). Conversely, the four 2.5 inch SSD slots are more general purpose in nature.
The point is that just because a NAS appliance has a vacant SSD slot, it does not necessarily mean that the slot is well suited to your intended purpose. Some slots may exist to serve a single, very specific purpose.
Does the Appliance Have Enough Memory?
In some ways, it seems odd to discuss memory in an article pertaining to SSD NAS requirements, but a NAS appliance’s available RAM can have a major impact on how the appliance can be used.
In the case of QNAP NAS appliances, for example, the available RAM actually determines the maximum size of an SSD cache. According to QNAP, a 512 GB SSD cache requires 1 GB of RAM. A NAS appliance with 8 GB of RAM can accommodate an SSD cache of up to 2 TB in size, and a 4 TB cache requires at least 16 GB of RAM.
The available memory can also impact your ability to create storage snapshots. The QNAP QTS series NAS appliances, for example, need 1 GB of RAM to create up to 32 snapshots, or 2 GB of RAM to create up to 64 snapshots. NAS appliances with 4 GB of RAM can create a far larger number of snapshots, but the actual number varies based on the CPU architecture.
Are Your Disks Well Suited to the Task at Hand?
Even if the SSDs that you plan to use are officially supported by the NAS vendor, you must consider whether they are well suited to the task at hand. QLC SSDs, for example, are relatively inexpensive, but also suffer from poor endurance, which means that they probably aren’t the best choice for NAS use. Conversely, Seagate’s IronWolf SSD has been specifically designed for NAS use, and includes features that are designed to ensure reliability and endurance.