Date: Tue, 23 Nov 2010 23:45:43 +1100 From: Andrew Reilly <areilly@bigpond.net.au> To: Jonathan Stewart <jonathan@kc8onw.net> Cc: stable@freebsd.org Subject: Re: ZFS backups: retrieving a few files? Message-ID: <20101123124543.GA4751@johnny.reilly.home> In-Reply-To: <4CEA8BA6.7080009@kc8onw.net> References: <20101122113541.GA74719@johnny.reilly.home> <4CEA8BA6.7080009@kc8onw.net>
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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 == level 0) and relative > >(incremental), and zfs send those to files on the backup disk. > > This is actively discouraged, there is no recovery ability when > receiving zfs streams so 1 bad bit would invalidate your entire backup. > > The currently accepted practice is to create a ZFS file system on the > backup drive and just keep sending incremental snapshots to it. As long > as the backup drive and host system have a snapshot in common you can do > 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 > 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= 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, -- Andrew
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