[OpenIndiana-discuss] measuring fragmentation on ZFS?

Brett Dikeman brett.dikeman at gmail.com
Mon Mar 14 20:10:25 UTC 2011

Is there a way to query how much fragmentation there is in a filesystem?

We've got a large filesystem which was allowed to get really full
before it was expanded considerably, and we also had deduplication
turned on briefly, which caused the dedupe table to get very, very
big.  While the application that stores data rewrites a lot of it, the
dedupe table still has a lot of entries in it, etc.

We can easily queue up data to move it between filesystems, and have
scratch space elsewhere, so I'm thinking of moving data off and then
back on again, but if there's a painless way to see how bad the
fragmentation is (and tell if moving data off+on again makes a
difference), I'd love to know.

PS:Thanks to those who replied about my earlier questions regarding
ZIL and L2ARC.  I've experimented with both- thanks!

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