On 03/01/2013 8:24 am, Karl Denninger wrote:
Dabbling with ZFS now, and giving some thought to how to handle backup
strategies.
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@unique-label
zfs send -i pool/some-filesystem@base
pool/some-filesystem@unique-label
zfs destroy pool/some-filesystem@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 briefly did something like this between two FreeNAS boxes, it seemed
to work well, but my secondary Box wasn't quite up to par hardware.
Combine that with the lack of necessary internet bandwidth with a second
physical location in case of something really disastrous, like a tornado
or fire destroying my house. I ended up just using an eSATA drive dock
and Bacula, with a few external drives rotated regularly into my office
at work, rather than upgrading the secondary box.
If you have the secondary box that is adequate, and either offsite
backups aren't a concern or you have a big enough pipe to a secondary
location that houses the backup this should work.
I would recommend testing your incremental snapshot rotation, I never
did test a restore from anything but the most recent set of data when I
was running my setup, I did however save a weeks worth of hourly
snapshots on a couple of the more rapidly changing data sets.
--
Thanks,
Dean E. Weimer
http://www.dweimer.net/
_______________________________________________
freebsd-stable@freebsd.org mailing list
http://lists.freebsd.org/mailman/listinfo/freebsd-stable
To unsubscribe, send any mail to "freebsd-stable-unsubscr...@freebsd.org"
