Date: Wed, 24 Mar 2010 23:27:12 +0100 From: Ivan Voras <ivoras@freebsd.org> To: freebsd-questions@freebsd.org Cc: freebsd-fs@freebsd.org Subject: Re: tuning vfs.zfs.vdev.max_pending and solving the issue of ZFS writes choking read IO Message-ID: <hoe3k0$tuk$2@dough.gmane.org> In-Reply-To: <cf9b1ee01003240918g3a7d61adqaeccb609090a09ea@mail.gmail.com> References: <cf9b1ee01003240918g3a7d61adqaeccb609090a09ea@mail.gmail.com>
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Dan Naumov wrote: > Hello > > I am having a slight issue (and judging by Google results, similar > issues have been seen by other FreeBSD and Solaris/OpenSolaris users) > with writes choking the read IO. The issue I am having is described > pretty well here: > http://opensolaris.org/jive/thread.jspa?threadID=106453 It seems that > under heavy write load, ZFS likes to aggregate a really huge amount of > data before actually writing it to disks, resulting in sudden 10+ > second stalls where it frantically tries to commit everything, > completely choking read IO in the process and sometimes even the > network (with a large enough write to a mirror pool using DD, I can > cause my SSH sessions to drop dead, without actually running out of > RAM. As soon as the data is committed, I can reconnect back). Mostly a wild guess, but can you test if this patch will help with choking your network and ssh: http://people.freebsd.org/~ivoras/diffs/spa.c.diff ? You can then fiddle with the vfs.zfs.zio_worker_threads_count loader tunable to see if it helps more.
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