Date: Sat, 21 Jan 2006 16:50:02 +0100 (CET) From: Oliver Fromme <olli@lurza.secnetix.de> To: freebsd-fs@FreeBSD.ORG Subject: Re: can snapshots become corrupted ? Is fsck'ing /dev/md0 sensible ? Message-ID: <200601211550.k0LFo2EN050245@lurza.secnetix.de> In-Reply-To: <20060120070110.80233.qmail@web50908.mail.yahoo.com>
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Joe Schmoe <non_secure@yahoo.com> wrote: > Let's say I have a running filesystem, and the system > crashes, and (for whatever reason) I mount and run the > filesystem in an unclean state. While in this > unclean, running state, I create a snapshot on it. > > Now let's say I unmount the filesystem and fsck it for > real. It gets marked clean. Is the snapshot that > resides on that filesystem still dirty ? Disclaimer: I haven't tried that, so this is just theory. Yes, the snapshot is probably still "dirty". But it shouldn't matter, because you can only mount it read-only anyway. > If so, is it expected that use of the clean FS with > the dirty snapshot enabled would cause system > instability (hard lock of system). It probably depends how "dirty" it is. If you had soft- updates enabled and the disk is reliable (i.e. not an IDE/ATA disk with write-cache enabled), then there are only unused blocks not marked as free. It is save to mount such a filesystem. But in all other cases, mounting a dirty filesystem read/write (forcibly) can indeed cause instability. It doesn't matter if snapshots are involved or not. > If so, is it sensible for me to mount the snapshot on > md0 and fsck /dev/md0 ? I don't think you can fsck a snapshot. Snapshots are read-only. Best regards Oliver -- Oliver Fromme, secnetix GmbH & Co. KG, Marktplatz 29, 85567 Grafing Dienstleistungen mit Schwerpunkt FreeBSD: http://www.secnetix.de/bsd Any opinions expressed in this message may be personal to the author and may not necessarily reflect the opinions of secnetix in any way. "The last good thing written in C was Franz Schubert's Symphony number 9." -- Erwin Dieterich
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