Date: Wed, 24 Mar 2010 15:47:59 -0500 (CDT) From: Bob Friesenhahn <bfriesen@simple.dallas.tx.us> To: Dan Nelson <dnelson@allantgroup.com> Cc: freebsd-fs@freebsd.org, Dan Naumov <dan.naumov@gmail.com>, freebsd-questions@freebsd.org Subject: Re: tuning vfs.zfs.vdev.max_pending and solving the issue of ZFS writes choking read IO Message-ID: <alpine.GSO.2.01.1003241545220.29281@freddy.simplesystems.org> In-Reply-To: <20100324175546.GF12330@dan.emsphone.com> References: <cf9b1ee01003240918g3a7d61adqaeccb609090a09ea@mail.gmail.com> <alpine.GSO.2.01.1003241212010.29281@freddy.simplesystems.org> <20100324175546.GF12330@dan.emsphone.com>
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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 -- Bob Friesenhahn bfriesen@simple.dallas.tx.us, http://www.simplesystems.org/users/bfriesen/ GraphicsMagick Maintainer, http://www.GraphicsMagick.org/
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