[OpenIndiana-discuss] ZFS pool slow as molasses

[Albert Lee]

On Tue, Oct 5, 2010 at 9:11 PM, Chris Mosetick <cmosetick at gmail.com> wrote:
> If it's not too late already, my suggestion at this point is to go back to
> ide mode in the bios, boot the machine and rsync your data to another
> physical machine through the network, then do a clean install of openindiana
> with your bios set to ahci mode, create new pools, then rsync your data back
> to the new pools.  Time consuming, yes.  But virtually guaranteed to work.
>
> It would seem that this machine would have worked better with ahci mode when
> you first installed opensolaris on it back in the day.  This is a lesson for
> everyone to check their bios settings thoroughly before installing a new
> operating system.

Erm, that's a curious bit of modern folklore. How the drive was
connected previously changes absolutely nothing.

The problem here is probably from having dedup enabled. Disabling it
does not affect the existing data, which has already been
deduplicated. Reading any of this will incur a deduplication table
lookup, which can be quite expensive in terms of random seeks (you can
check with DTrace, see /opt/DTT/disk/seeksize.d). I've also seen poor
performance on a pool that was previously full.

-Albert