5 ms·

is 90% used space even good with ZFS these days? I always reserve 25% in order to keep fragmentation in check

• Filligree 4y ago
  It really depends on how much performance you want. And don’t forget that 10% of a disk is a lot more space than it used to be.
• magicalhippo 4y ago
  It's not just keeping fragmentation in check, above a threshold ZFS switches allocation strategy. The "nearly full" allocator is typically slower, IIRC because it tries to find better fitting free-space holes than the default allocator. I can't recall if the threshold is 80% or 90% right now, but around there.
  • rincebrain 4y ago
    It is, I believe, 96% full in the spacemap for it to resort to best-fit instead of first-fit. [1] [1] - https://github.com/openzfs/zfs/blob/eaaed26ffb3a14c0c98ce1e6e039e62327ab4447/module/zfs/metaslab.c#L166-L172 https://github.com/openzfs/zfs/blob/eaaed26ffb3a14c0c98ce1e6...
• rsync 4y ago
  "is 90% used space even good with ZFS these days?" Yes, you can run busy zpools with many different random access consumers at 90%. I wouldn't do it without a SLOG but it is really only at 92%, these days, that we start to see performance really degrade. YMMV.
  • rincebrain 4y ago
    In theory, the dedicated log metaslab[1] feature should help avoid that sort of problem in the same way, I think, and is in 2.1, with no slog required. I'd be curious if you're suggesting you're running something based on 2.1 and still finding you can run it fuller more reasonably. [1] - https://github.com/openzfs/zfs/commit/aa755b35493a2d27dbbc59f1527c6c93788b28f6 https://github.com/openzfs/zfs/commit/aa755b35493a2d27dbbc59...