Date: Sat, 2 Oct 2021 11:54:40 +0100 From: Steve O'Hara-Smith <steve@sohara.org> To: David Christensen <dpchrist@holgerdanske.com> Cc: freebsd-questions@freebsd.org Subject: Re: zfs q regarding backup strategy Message-ID: <20211002115440.85c4342a49fe6e4573c37dd0@sohara.org> In-Reply-To: <809e4f3b-9e59-eb53-5b7d-0bcf7e401cd5@holgerdanske.com> References: <YVZM1HnPuwIUQpah@ceres.zyxst.net> <ba54a415-da45-e662-73fe-65702c4131e2@holgerdanske.com> <YVcXsF5NFq2abE%2B7@ceres.zyxst.net> <20211001222816.a36e9acbd4e8829aed3afb68@sohara.org> <809e4f3b-9e59-eb53-5b7d-0bcf7e401cd5@holgerdanske.com>
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On Fri, 1 Oct 2021 16:10:44 -0700 David Christensen <dpchrist@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 settings. 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@sohara.org>
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