Date: Tue, 23 Nov 2010 10:35:27 -0800 From: "Malcolm Waltz" <mwaltz@PACIFIC.EDU> To: "Andrew Reilly" <areilly@bigpond.net.au> Cc: stable@freebsd.org Subject: RE: ZFS backups: retrieving a few files? Message-ID: <2A40FCBD209C654588C3F74D5BFF2C7C07B5468A@EXVS2.stk.pacific.edu> In-Reply-To: <20101123124543.GA4751@johnny.reilly.home> References: <20101122113541.GA74719@johnny.reilly.home><4CEA8BA6.7080009@kc8onw.net> <20101123124543.GA4751@johnny.reilly.home>
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If you end up in the double-mounted situation mentioned below, use "mount -v" to find the fsid for each double-mounted filesystem and then umount them using the fsid. To avoid this, always use the "-R" option (temporary, alternate root mount point) with zpool if you are working with a root pool. This also applies if you boot off of a CD or DVD and want to examine or modify a root pool. FWIW, I have successfully tested a bare metal restore from ZFS "full" and "incremental" send/receive backups (from an NFS mount off of a DataDomain). So, risks aside, it does work. I believe gzipped tar files would also fail if a bit flipped. -----Original Message----- From: owner-freebsd-stable@freebsd.org [mailto:owner-freebsd-stable@freebsd.org] On Behalf Of Andrew Reilly Sent: Tuesday, November 23, 2010 4:46 AM To: Jonathan Stewart Cc: stable@freebsd.org Subject: Re: ZFS backups: retrieving a few files? On Mon, Nov 22, 2010 at 10:26:30AM -0500, Jonathan Stewart wrote: > On 11/22/2010 6:35 AM, Andrew Reilly wrote: > >Dump/restore doesn't work for ZFS. I *think* that I'm running > >backups in the appropriate equivalent fashion: I take file > >system snapshots (both absolute =3D=3D level 0) and relative > >(incremental), and zfs send those to files on the backup disk. >=20 > This is actively discouraged, there is no recovery ability when=20 > receiving zfs streams so 1 bad bit would invalidate your entire backup. >=20 > The currently accepted practice is to create a ZFS file system on the=20 > backup drive and just keep sending incremental snapshots to it. As long=20 > as the backup drive and host system have a snapshot in common you can do=20 > incremental transfers. This way you only have to keep the most recent > snapshot on the main system and can keep as many as you have space for > on the backup drive. You also have direct access to any backed up=20 > version of every file. For those playing along at home, I'll issue a small warning, based on today's frolics: Say, for example, one had done a: zfs send -vR tank/home@0 | zfs receive -d /backup/snapshots in order to experiment with this strategy. One would then become alarmed when one discovered that the receive mechanism also invoked the mountpoint=3D parameter of the source filesystem, and the zfs propensity for just doing stuff, and boom: you have a read-only version of your home directory mounted *on top of* your actual home directory... Required a reboot to single user mode, to go in and reset the mountpoint setting for the newly created file system (by way of hitting the power switch, after using zfs unmount -f to royally screw things up, preventing subsequent network logins.) Left wondering how to manage that change as part of an automated backup schedule. I think that this backup strategy has a few sharp edges... No, I don't like tar, rsync and friends for backups: they don't deal well with hard links, special files or sparse files. Cheers, --=20 Andrew _______________________________________________ freebsd-stable@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-stable To unsubscribe, send any mail to "freebsd-stable-unsubscribe@freebsd.org"
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