tuning vfs.zfs.vdev.max_pending and solving the issue of ZFS writes choking read IO

Bob Friesenhahn bfriesen at simple.dallas.tx.us
Wed Mar 24 20:48:09 UTC 2010

On Wed, 24 Mar 2010, Dan Nelson wrote:
> I had similar problems on a 32GB Solaris server at work.  Note that with
> compression enabled, the entire system pauses while it compresses the
> outgoing block of data.  It's just a fraction of a second, but long enough
> for end-users to complain about bad performance in X sessions.  I had to
> throttle back to a 256MB write limit size to make the stuttering go away
> completely.  It didn't affect write throughput much at all.

Apparently this was a kernel thread priority problem in Solaris.  It 
is apparently fixed in recent versions of OpenSolaris.  The fix 
required adding a scheduling class which allowed the kernel thread 
doing the compression to be less than the priority of normal user 
processes (such as the X11 server).

Bob Friesenhahn
bfriesen at simple.dallas.tx.us, http://www.simplesystems.org/users/bfriesen/
GraphicsMagick Maintainer,    http://www.GraphicsMagick.org/

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