Date: Tue, 17 May 2011 14:55:54 +0300 From: Andriy Gapon <avg@FreeBSD.org> To: Jeremy Chadwick <freebsd@jdc.parodius.com> Cc: Charles Sprickman <spork@bway.net>, stable@FreeBSD.org Subject: Re: 8.1R possible zfs snapshot livelock? Message-ID: <4DD2624A.9080708@FreeBSD.org> In-Reply-To: <20110517112952.GA48610@icarus.home.lan> References: <alpine.OSX.2.00.1105170120510.1983@hotlap.nat.fasttrackmonkey.com> <20110517073029.GA44359@icarus.home.lan> <4DD25264.8040305@FreeBSD.org> <20110517112952.GA48610@icarus.home.lan>
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on 17/05/2011 14:29 Jeremy Chadwick said the following: > On Tue, May 17, 2011 at 01:48:04PM +0300, Andriy Gapon wrote: >> on 17/05/2011 10:30 Jeremy Chadwick said the following: >>> On Tue, May 17, 2011 at 02:43:44AM -0400, Charles Sprickman wrote: >>>> Does this sound familiar to anyone running ZFS with snapshots? >>> >>> Yes, and is exactly why I don't use them. :-) >> >> You put a smiley, but is this an attempt at FUD? > > I wish it were. The reason I asked is that I could have easily answered "No, that's why I use them all the time". And I am sure many people would join me on this. So the way you originally described the issue was sufficiently non-specific and strong. > I experienced similar behaviour to Charles during the > early 8.x days (possibly 8.1-RELEASE, I forget; I may be thinking of > 8.0?) where ZFS snapshots would occasionally result in the kernel > deadlocking on ZFS-bound I/O. The kernel was alive/responsive to some > degree but ZFS I/O would just indefinitely stall at that point, > requiring a full system reset. No disk or controller problems (same > hardware I'm using today actually!). > > I believe there were commits and improvements for snapshotting committed > between 8.1-RELEASE and 8.2-RELEASE, but I haven't bothered to test > them. The experience left a very bad taste in my mouth and as such I > have avoided ZFS snapshots since. > > I'd be willing to try them again assuming someone can at least confirm > that there were commits done to address snapshot concerns during the > past year or so. But... > > There are still some outstanding incidents that directly pertain to ZFS > snapshots, or are "related" to ZFS snapshots (meaning things like > send/recv which are commonly used alongside snapshots), which I remember > reading about but really saw no answer to: > > * ZFS send | ssh zfs recv results in ZFS subsystem hanging; 8.1-RELEASE; > February 2011: > http://lists.freebsd.org/pipermail/freebsd-fs/2011-February/010602.html > > * Kernel panic during heavy disk I/O while "zfs recv" being used > simultaneously; CURRENT (so ZFS v28?); April 2011: > http://lists.freebsd.org/pipermail/freebsd-fs/2011-April/011155.html > > * ZFS snapshots taking an extremely long time to be deleted; RELENG_8_1; > February 2011: > http://lists.freebsd.org/pipermail/freebsd-fs/2011-February/010797.html > > * "zfs destroy -r" not working on filesystem-level snapshots but works > on pool-level snapshots; RELENG_8 with ZFS v28 patch (and is specific > to ZFS v28 given the info); May 2011: > http://lists.freebsd.org/pipermail/freebsd-fs/2011-May/011412.html > > Sorry to just rattle off a bunch of URLs and issues at once; it's not my > intention to slander work on ZFS or anything even remotely like that. > > I'm just wondering given the number of problem reports that seem to come > in about snapshot or snapshot-related ZFS stuff, where we stand on > these? This is mainly for Charles' benefit and not so much mine (our > rsnapshot/rsync-based backups work great for us at this time, sans the > stomping of atime). > Problem reports are always over-represented on the mailing lists. People rarely write that e.g. ZFS snapshot has flawlessly worked for them for the millionth time again today. I am not aware of any known-but-not-fixed issues in this area. Each problem report should be properly investigated individually. -- Andriy Gapon
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