Musings on ZFS Backup strategies
ronald-freebsd8 at klop.yi.org
Fri Mar 1 15:06:11 UTC 2013
On Fri, 01 Mar 2013 15:24:53 +0100, Karl Denninger <karl at denninger.net>
> Dabbling with ZFS now, and giving some thought to how to handle backup
> ZFS' snapshot capabilities have forced me to re-think the way that I've
> handled this. Previously near-line (and offline) backup was focused on
> being able to handle both disasters (e.g. RAID adapter goes nuts and
> scribbles on the entire contents of the array), a double-disk (or worse)
> failure, or the obvious (e.g. fire, etc) along with the "aw crap, I just
> rm -rf'd something I'd rather not!"
> ZFS makes snapshots very cheap, which means you can resolve the "aw
> crap" situation without resorting to backups at all. This turns the
> backup situation into a disaster recovery one.
> And that in turn seems to say that the ideal strategy looks more like:
> Take a base snapshot immediately and zfs send it to offline storage.
> Take an incremental at some interval (appropriate for disaster recovery)
> and zfs send THAT to stable storage.
> If I then restore the base and snapshot, I get back to where I was when
> the latest snapshot was taken. I don't need to keep the incremental
> snapshot for longer than it takes to zfs send it, so I can do:
> zfs snapshot pool/some-filesystem at unique-label
> zfs send -i pool/some-filesystem at base pool/some-filesystem at unique-label
> zfs destroy pool/some-filesystem at unique-label
> and that seems to work (and restore) just fine.
> Am I looking at this the right way here? Provided that the base backup
> and incremental are both readable, it appears that I have the disaster
> case covered, and the online snapshot increments and retention are
> easily adjusted and cover the "oops" situations without having to resort
> to the backups at all.
> This in turn means that keeping more than two incremental dumps offline
> has little or no value; the second merely being taken to insure that
> there is always at least one that has been written to completion without
> error to apply on top of the base. That in turn makes the backup
> storage requirement based only on entropy in the filesystem and not time
> (where the "tower of Hanoi" style dump hierarchy imposed both a time AND
> entropy cost on backup media.)
> Am I missing something here?
> (Yes, I know, I've been a ZFS resister.... ;-))
I do the same. I only use zfs send -I (capital i) so I have all the
snapshots on the backup also.
That way the data survives an oops (rm -r) and a fire at the same time. :-)
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