Date: Wed, 11 Nov 2009 14:49:03 -0600 From: Dan Nelson <dnelson@allantgroup.com> To: Ivan Voras <ivoras@freebsd.org> Cc: freebsd-current@freebsd.org Subject: Re: Help ZFS FreeBSD 8.0 RC2 Write performance issue Message-ID: <20091111204903.GI89052@dan.emsphone.com> In-Reply-To: <hdf23m$b6n$1@ger.gmane.org> References: <11167f520911111050j36dd94far667c81e6f5c18e69@mail.gmail.com> <hdf23m$b6n$1@ger.gmane.org>
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In the last episode (Nov 11), Ivan Voras said: > Sam Fourman Jr. wrote: > > I am running FreeBSD 8.0RC2 and I dont understand why my ZFS/NFS is > > acting weird on writes. I get ~150mbit writes idk if this is good or > > not? but it paused for a few seconds every once and awhile. > > You didn't give any "iostat" statistics - I suspect that if you > correlate ifstat and iostat output that you will see that network > "pauses" happen during spikes in IO. You should check for this and post > your results. Yes, iostat would be useful here. "iostat -zxC 2" will give you per-disk stats plus CPU usage every 2 seconds (CPU may be a factor if you have compression enabled). On a Solaris box I admin, setting zfs_write_limit_override helped stuttering while doing heavy writes. It's not exported on FreeBSD, but it should be easy to add it as a RW sysctl; it lives in dsl_pool.c and can be tweaked at runtime. Start big and tune it down so each write burst takes under a second; it looks like you're writing solid for around 6-8 seconds now. The number will vary depending on your disk speed and how much ARC you have. -- Dan Nelson dnelson@allantgroup.com
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