Re:Demystifying OpenZFS 2.0
by rincebrain on Friday November 19, 2021 @02:01AM
(#29274547)
I haven't tried Nexenta in a long long time, but it seems like it was part of their allocation classes code [1]. The comment at the top of the file says the implementation there doesn't support WBC, but [2] seems to suggest otherwise...
So if you really wanted to, you could try looting code from there, though I believe Nexenta's implementation of that was either orthogonal or significantly different from the one that landed in OpenZFS...
[1] - https://github.com/Nexenta/illumos-nexenta/blob/release-5.3/...
[2] - https://github.com/Nexenta/illumos-nexenta/blob/release-5.3/...
Exactly, and it's even worse. By default ZFS only stores about 5 seconds worth of writes in the ZIL, so if you have a NAS with say a 10Gbe link that's less than 10GB in the ZIL (and hence SLOG) at any time.
> A real write cache would be awesome for ZFS.
Agreed. It's a real shame the write-back cache code never got merged, I think it's one of the major weaknesses of ZFS today.