> 6.8 Flush command
> …
> If a volatile write cache is not present or not enabled, then Flush commands shall complete successfully and have no effect.
And:
> 5.21.1.6 Volatile Write Cache
> …
> Note: If the controller is able to guarantee that data present in a write cache is written to non-volatile media on loss of power, then that write cache is considered non-volatile and this feature does not apply to that write cache.
A specific somewhat dated example: Samsung 980 Pro (consumer client), PM9A1 (OEM client), and PM9A3 (datacenter) are very similar drives that have the same PCI ID and are all available as M.2. PM9A3 drives have power loss protection and the others don’t. It has very consistent write latency (on the order of 20 - 50 μs when not exceptionally busy) and very consistent throughput (up to 1.5 GB/s) regardless of how full it is. The same cannot be said of the client drives without PLP but with tricks like TurboWrite (aka pseudo-SLC). When more than 30% of the NAND is erased, the client drives can take writes at 5 GB/s but that rate falls off a cliff and gets wobbly when the pseudo-SLC cache fills.
jauntywundrkind•1mo ago