Date: Thu, 18 Aug 2005 08:26:33 -0400 (EDT) From: Daniel Feenberg <feenberg@nber.org> To: Giorgos Keramidas <keramida@ceid.upatras.gr> Cc: Mohan Ramanujan <mohan@nber.org>, Alex Aminoff <aminoff@nber.org>, freebsd-questions@freebsd.org Subject: Re: Making UFS snapshots Message-ID: <Pine.GSO.4.10.10508180724380.9852-100000@nber5.nber.org> In-Reply-To: <20050818112828.GA1282@flame.pc>
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On Thu, 18 Aug 2005, Giorgos Keramidas wrote: > On 2005-08-17 16:32, Daniel Feenberg <feenberg@nber.org> wrote: > > > > I notice on this list that Garance Drosehn > > <http://docs.FreeBSD.org/cgi/mid.cgi?p06230924bf1c752ccf7f>; reports making > > a snapshot of a 4 gigabyte filesystem in less than one second. We have a > > 859 gigabyte filesystem and snapshots take about 75 minutes to complete. > > Making a snapshot is not very slow if the disk is relatively idle at the > time. Perhaps this is what's biting you? The computer and the disk system is otherwise idle - no activity other than taking the snapshot. Since the original posting I found Dr McKusik's 1999 Usenix paper describing snapshots which suggests the time for taking a snapshot should be "brief", and that file system activity should resume after a time no longer than that required for an unmount. This suggests to me that something is wrong with our setup, but I still have no idea what. However, I have found some messages from users with experience similar to ours e.g. http://www.mail-archive.com/freebsd-stable@freebsd.org/msg67320.html Dan Feenberg feenberg isat nber dotte org 617-588-0343 > >
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