zfs q regarding backup strategy
steve at sohara.org
Sat Oct 2 10:54:55 UTC 2021
On Fri, 1 Oct 2021 16:10:44 -0700
David Christensen <dpchrist at holgerdanske.com> wrote:
> On 10/1/21 14:28, Steve O'Hara-Smith wrote:
> The one time I tried booting a system with two OS drives, two boot
> pools, and two root pools convinced me to never to try that again.
Been there, done that, rebuilt the system!
> My backup plan for OS instances is to take an image of the device with
> dd(1). For this reason, I keep my OS instances small enough to fit on
> "16 GB" devices and use one device per OS instance.
Sounds like a good strategy, I'm relying on mirrors and simplicity
for OS images currently.
> > Also there is the
> > irritating detail that one of the properties of a ZFS filesystem is its
> > mount point and while you can run zfs recv in such a way as not to mount
> > the received filesystems they will get mounted on reboot which makes
> > backing up several root filesystems to an archive server a little
> > tricky!
> Are you referring to the zpool(8) property 'altroot'?
If only it were a persistent property it would be more useful and
if it were available at filesystem level.
> I recall that FreeNAS uses altroot, and it is persistent across reboots.
Oh now that's a neat trick.
> I wonder how they accomplished that? Import scripts on boot and
> export scripts on shutdown? But, how to deal with an unclean shutdown
> and/or failed export? STFW I do not see any clues.
Thinking about it I'd guess they register the altroot in some
database (append to a text file perhaps) at the time they set it on
receiving the initial stream for the filesystem and creating the
filesystem, then as you say use a boot time script to restore the altroot
I wonder if the FreeNAS solution is available for use, I only see
some python libraries in the ports.
> Perhaps a top-level "archive" pool, one ZFS volume per <source>, one
> pool per volume, and some work-around to achieve persistent altroot's (?).
A separate pool for each archive ? I don't like that pools are
rather inflexible things, I rather want to share that stack of big disks.
Steve O'Hara-Smith <steve at sohara.org>
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