Date: Thu, 25 May 2006 17:53:15 -0400 From: Kris Kennaway <kris@obsecurity.org> To: Eric Anderson <anderson@centtech.com> Cc: freebsd-fs@freebsd.org, Kris Kennaway <kris@obsecurity.org> Subject: Re: Access to UFS stuck during snapshot. Message-ID: <20060525215314.GA31540@xor.obsecurity.org> In-Reply-To: <44744EF8.2000000@centtech.com> References: <4473FA8F.6050102@outblaze.com> <20060524061848.GA58522@xor.obsecurity.org> <44744EF8.2000000@centtech.com>
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[-- Attachment #1 --] On Wed, May 24, 2006 at 07:18:00AM -0500, Eric Anderson wrote: > Kris Kennaway wrote: > >On Wed, May 24, 2006 at 02:17:51PM +0800, Kent Ho wrote: > >>Hi, > >> > >>I having problems accessing file system during snapshot runs. snapshot > >>takes approximately 10 to 20 mins to run. > >> > >>During that time access to files in the file system are blocked until > >>the snapshot has completed. Lot of processes was stuck and piles up on > >>the fs. > >> > >>This fs stores mailboxes and it's accessed 24/7. This is similar to > >>what described in this thread. > >> > >>http://www.freebsd.org/cgi/getmsg.cgi?fetch=14968+0+/usr/local/www/db/text/2006/freebsd-fs/20060312.freebsd-fs > >> > >>Has this been improved or fixed in recent releases, I see a bunch of > >>fixes in march? any possible work around? any alternatives or > >>recommendations? Looking for high availability fs with snapshots. > > > >It's by design. > > > >Kris > > I found that making the .snap directories permissions 0700, and then > making a subdirectory under the .snap that stores the actual snapshots > helped, as long as I did not make any stat() calls to the snapshot file > that was in snaplk state. > > Kris - you've had your head deep in the snapshot spaghetti recently - is > this blocking just a matter of the locking on the snapshot file and a > stat() call blocking on it, which causes an upward locking to the root > dir of the filesystem? Could this be avoided by 'hiding' the snapshot > file while a snapshot is in progress? I have been tinkering with hiding > the snapshot directory during snapshot creation, but I don't have any > results of anything yet, still too early. I'm a wannabe hacker, so my > progress is slow. No, I/O is suspended while the snapshot is being created. As I said, it's a design limitation. Kris [-- Attachment #2 --] -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.3 (FreeBSD) iD8DBQFEdidKWry0BWjoQKURAjlZAJ9KPtP0FOBiV/F+JtnqfHZitSS1gACglL+T aqnKfcAMTqJBsFoqdNbjb0Y= =O6BU -----END PGP SIGNATURE-----
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