> > Disks that have been in use for a longer time may have very fragmented free
> > space on one hand, and not so much of it on another, but ZFS is still 
> > trying to push
> > bits around evenly. And while it's waiting on some disks, others may be 
> > blocked as
> > well. Something like that...
> This could explain why performance would go up after a large delete but I've 
> not 
> seen large wait times for any of my disks. The service time, percent busy, 
> and 
> every other metric continues to show nearly idle disks.

I believe, in this situation the older fuller disks would show some activity 
and others can show zero or few IOs - because ZFS has no tasks for them. It 
sent a series of blocks to write from the queue, newer disks wrote them and 
stay dormant, while older disks seek around to fit that piece of data... When 
old disks complete the writes, ZFS batches them a new set of tasks.

> If this is the problem- it would be nice if there were a simple zfs or dtrace 
> query 
> that would show it to you.

Well, it seems that the bridge between email and web interfaces to OpenSolaris 
forums has been fixed, for new posts at least, and hopefully Richard Elling or 
some other experts would come up with an idea of a dtrace for your situation.

I have little non-zero hope that the experts would also come to the web-forums 
and review the past month's posts and give their comments to my, your and 
others' questions and findings ;)

//Jim Klimov
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