Comment by dboreham

4 years ago

Surprised this is being rediscovered. Years ago only "enterprise" or "data center" SSDs had the supercap necessary to provide power for the controller to finish pending writes. Did we ever expect consumer SSDs to not lose writes on power fail?

19 comments

dboreham

Reply
evancox100  4 years ago

It's not losing pending writes, it's the drive saying there are no pending writes, but losing them anyways. ie the drive is most likely lying

  • monocasa  4 years ago

    As I said in the recent Apple discussion, pretty much all drives are lying and have been for decades at this point. The good brands just spec out enough capacitance that you don't see the difference externally.

    https://news.ycombinator.com/item?id=30370551#30374585

    • WrtCdEvrydy  4 years ago

      The more you look at speculative execution and these drive issues, the more you see that we're giving up a lot of what computing "safe" for just performance.

      2 replies →

    • brigade  4 years ago

      So if SSDs rely solely on capacitors for data integrity and lie about flushes, what do they do on a flush that takes any amount of time? Are they just taking a speed hit for funsies? Heck, from this test, the magnitude of the speed hit isn't even correlated with whether they lose writes...

      3 replies →

    • fire  4 years ago

      Any ides how one finds out whether a drive is actually capped properly to handle power off data loss?

phkahler  4 years ago

This is not about pulling power during writes. Flush is supposed to force all non-committed (i.e. cached) writes to complete. Once that has been acknowledged there is no need for any further writes. So those drives are effectively lying about having completed the flush. I also have to wonder when they intended to write the data...