logoalt Hacker News

moffkalastyesterday at 5:36 PM1 replyview on HN

That's not something you can do reliably in software, datacenter grade NVMe drives come with power loss protection and additional capacitors to handle that gracefully. If power is cut at the wrong moment the partition may not be mountable afterwards otherwise.

If you really live somewhere with frequent outages, buy an industrial drive that has a PLP rating. Or get a UPS, they tend to be cheaper.


Replies

croteyesterday at 6:02 PM

Isn't that the entire point of write-ahead logs, journaling file systems, and fsync in general? A roll-back or roll-forward due to a power loss causing a partial write is completely expected, but surely consumer SSDs wouldn't just completely ignore fsync and blatantly lie that the data has been persisted?

As I understood it, the capacitors on datacenter-grade drives are to give it more flexibility, as it allows the drive to issue a successful write response for cached data: the capacitor guarantees that even with a power loss the write will still finish, so for all intents and purposes it has been persisted, so an fsync can return without having to wait on the actual flash itself, which greatly increases performance. Have I just completely misunderstood this?

show 3 replies