&quot;I&#x27;ve seen this repeated a lot, but have not had quite the same experience with &quot;permanent&quot; performance degradation. Especially if I eventually expand the pool with another vdev. Not sure about ZFSonLinux&quot;<p>Look, I&#x27;ll admit that we haven&#x27;t done a lot of scientific comparisons between healthy pools and presumed-wrecked-but-back-below-80-percent pools ... but I know what I saw.<p>I think if you break the 90% barrier and either:  a) get back below it quickly, or b) don&#x27;t do much on the filesystem while it&#x27;s above 90%, you&#x27;ll probably be just fine once you get back below 90%.  However, if you&#x27;ve got a busy, busy, churning filesystem, and you grow above 90% <i>and you keep on churning it</i> while above 90%, your performance problems will continue one you go back below, presuming the workload is constant.<p>Which makes sense ... and, anecdotally, is the same behavior we saw with UFS2 when we tune2fs&#x27;d minfree down to 0% and ran on that for a while ... freeing up space and setting minfree back to 5-6% didn&#x27;t make things go back to normal ...<p>I am receptive to the idea that a ZIL solves this.  I don&#x27;t know if it does or not.