Do you need an SSD cache in a NAS?

When a cache helps — and when it does nothing

A read cache holds recently or frequently accessed data on fast flash. It helps when your access pattern re-reads the same data: working on the same project files, browsing a photo library, running containers whose images and databases are hit constantly. It does nothing for a one-pass workload — streaming a movie you watch once, or a nightly backup that writes and never re-reads. Be honest about your pattern before buying flash for cache.

Your network usually matters more

A cache cannot make the NAS faster than the link to it. On gigabit (~110 MB/s) a single hard drive already saturates the connection, so a cache adds nothing you will notice. The maths only changes on 2.5GbE (~280 MB/s) or 10GbE (~1,100 MB/s), where a hard-drive array cannot keep the pipe full and a cache — or an NVMe pool — starts to earn its slot. If your NAS is on gigabit, upgrade the network before you buy cache flash.

If you do add one

Use an NVMe SSD with a real TBW rating, not a cheap DRAM-less drive — a write cache wears flash faster than normal use. On Synology, note the drive-list catch: an NVMe cache or pool still requires a Synology SNV3400/SNV5400 even after the DSM 7.3 relaxation, which covered only hard drives and SATA SSDs. On UGREEN, QNAP and DIY, any quality NVMe works.

Buying in Canada

Canadians cross-shop Amazon.ca, Best Buy Canada, Canada Computers, Newegg.ca and Memory Express; the cheapest SKU moves between them, and we track Amazon.ca live in CAD as the baseline. It is worth a two-minute check across those before you buy a drive or a NAS.

On importing from Amazon.com: it rarely beats a local CAD price once you add exchange, any duty, brokerage and the harder path to a warranty claim or return. The exchange rate is not a penalty — the honest point is total landed cost plus how much easier a return or RMA is when you bought it in Canada. For a drive that will run 24/7 for years, local warranty support is worth real money.