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 imp

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/usr/src/uts/common/fs/zfs/special.c https://github.com/Nexenta/illumos-nexenta/blob/release-5.3/... [2] - https://github.com/Nexenta/illumos-nexenta/blob/release-5.3/usr/src/common/zfs/zpool_prop.c#L214 https://github.com/Nexenta/illumos-nexenta/blob/release-5.3/...