Solid-state drive (SSD) caching inside network-attached storage (NAS) is when a flash drive is used by the operating system as slower RAM to improve the performance of installed drives. It's worth considering when you cannot expand the amount of RAM available to the system, plan on running resource-intensive applications such as virtual machines, have multiple accounts accessing the NAS at any given time, and work with many smaller files such as photos. SSD caching can be expensive and it's not required with every NAS enclosure.
5 Improves system responsiveness
The OS will feel faster
Like Windows, your NAS OS can feel sluggish when there aren't enough system resources to handle all the tasks sent to the hardware. That's where SSD caching can come into play. By improving the storage pool performance, your OS may benefit from storing more data in RAM and on the caching drive for quicker access. The result should be a snappier web GUI, quicker access to various installed apps, and an overall more pleasant experience. The primary goal of SSD caching is to provide your NAS with additional bandwidth and remove any bottlenecks relating to memory and storage.
4 Masks the speed limit of hard drives
Farewell SATA III limits
Hard drives inside NAS are slow, but they're reliable for storing lots of data. And by slow, I don't mean they're terrible for running containers, virtual machines, and other tasks, but you will have to wait slightly longer for things to load than you would an SSD. With caching enabled on the NAS OS and a drive or two dedicated to this feature, you should notice a significant uptick in performance, especially with files you frequently use and drives spinning with slower motors. Virtual machines should run faster, as well as the underlying OS and any native apps that may be installed and running. Transfers should improve, though this will be limited by your network and the LAN ports.
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3 If your NAS is already at RAM capacity
A great alternative to RAM
Unable to upgrade or expand the RAM inside your NAS? That's where SSD caching makes the most sense. RAM is still faster (and cheaper) for improving the performance of your NAS by providing the CPU with more memory. However, when you're at maximum memory capacity, that's where an SSD caching drive will lend a hand. Unused RAM is wasteful, so it's okay for the OS to allocate most of your system memory to ensure rapid responses. SSD caching works by expanding this memory with slower speeds but helps overcome HDD bottlenecks.
2 Prep the NAS for non-storage tasks
Running VMs and more
Looking to run a virtual machine on your NAS? That's possible! These powerful enclosures can even run surveillance centers, media servers, and much more. They're more servers than simple NAS and that's where more RAM and SSD caching can help. The latter is great for allowing the OS to access frequently used data quicker than a standard HDD. If you boot up the same VM daily, this can have a positive impact on the performance. The same goes for photos, services (web servers, game servers, etc.), and general data movement. Even using the NAS for storing your game library can make SSD caching worthwhile.
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1 Additional data loss protection
You're still protected by caching
Reading and writing data using SSD caching is as secure as a RAID. Should you encounter issues with the SSD while it's moving data, the OS should be able to route all traffic to the main array of storage drives to avoid data loss. Similar rules apply to caching SSDs as regular storage pools, though you should expect a long lifespan for rated drives in such a configuration. Although the SSDs set to caching will see lots of data being written, you shouldn't come near the TBW endurance rating unless it's a cheap drive or you're using the NAS extensively.
Should you use SSD caching?
This comes down to whether your NAS supports SSD caching, if you have already hit the memory capacity, and if it will make a difference. Not all NAS enclosures have free SSD slots for caching. While using one of the available drive bays is possible, I recommend against this as you're limiting the raw capacity for storing data. M.2 SSD slots are the better option for cache drives. Next, upgrading RAM before using cache can lead to similar results and be the cheaper option. Finally, if you don't push your NAS and its internal components hard enough, you may not see the benefits of using an SSD cache.