Date: Tue, 23 Nov 2010 14:49:50 -0500 From: Kurt Lidl <lidl@pix.net> To: Chris St Denis <chris@smartt.com> Cc: freebsd-hackers@freebsd.org Subject: Re: UFS Snapshots and iowait Message-ID: <20101123194950.GB74848@pix.net> In-Reply-To: <4CEC0A27.8080900@smartt.com> References: <4CEC0A27.8080900@smartt.com>
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On Tue, Nov 23, 2010 at 10:38:31AM -0800, Chris St Denis wrote: > Is this just due to the very high io bandwidth usage associated with > making a snapshot, or does the creation of this snapshot completely > block IO writes for around 5 minutes? It blocks updates to the filesystem while during part of the snapshot process. See the comments in /usr/src/sys/ufs/ffs/ffs_snapshot.c I found using UFS snapshots on a production fileserver untenable during normal working hours. I have a backup fileserver that I rsync the files to, and then use the UFS snapshots there. > Any suggested workarounds? I already bumped up the number of Apache > slots to 166% but it looks like I would have to increase the number much > more to use that as a primary solution. Use ZFS. The way snapshots work there, they are nearly instantanous to create, and you are not limited to 20 snapshots per filesystem. -Kurt
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