Date: Tue, 23 Nov 2010 10:38:31 -0800 From: Chris St Denis <chris@smartt.com> To: freebsd-hackers@freebsd.org Subject: UFS Snapshots and iowait Message-ID: <4CEC0A27.8080900@smartt.com>
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I have started using "mount -u -o snapshot" as part of my backup process in order to have a week worth of local differential backups to allow quick and easy recovery of lost/overwritten/etc files. The snapshot of the partition (~250G and 2.3 million inodes used. ~10GB of data change per day) takes around 10 minutes to complete. During the first 5 minutes everything seems to be find, but during the second 5 minutes the Apache processes that are logging to this drive start building up in L (logging) state until they hit MaxClients. 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? 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.
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