Date: Mon, 23 Jan 2012 23:39:10 +0100 From: Andreas Nilsson <andrnils@gmail.com> To: "Christopher J. Ruwe" <cjr@cruwe.de> Cc: freebsd-fs@freebsd.org Subject: Re: Booting from zfs snapshot Message-ID: <CAPS9%2BSv7m0p-V1xUYxP2TZmu74iEfEMmrQm1MV4U7R4OtNmeww@mail.gmail.com> In-Reply-To: <20120123224717.55de7481@dijkstra> References: <CAPS9%2BSsyvw=Day%2B1XC8HmzWQG3M=GZE=Nt-qaEQiQTPYME9MrA@mail.gmail.com> <jfgv8j$82s$1@dough.gmane.org> <CAPS9%2BSvtYZt1m26jCqRH6c3w_aB3hWt56ZFoYJAw_cEu2NANzg@mail.gmail.com> <jfjlhq$p77$1@dough.gmane.org> <CAPS9%2BSvA8c=uY7b%2BeKMrA2CnFS4Kg1ccxgaVYm9RSZy1GQ6ChA@mail.gmail.com> <20120123224717.55de7481@dijkstra>
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On Mon, Jan 23, 2012 at 10:47 PM, Christopher J. Ruwe <cjr@cruwe.de> wrote: > On Mon, 23 Jan 2012 14:42:19 +0100 > Andreas Nilsson <andrnils@gmail.com> wrote: > > > On Mon, Jan 23, 2012 at 1:58 PM, Johannes Totz <johannes@jo-t.de> > > wrote: > > > > > On 22/01/2012 20:15, Andreas Nilsson wrote: > > > > > >> On Sun, Jan 22, 2012 at 1:25 PM, Johannes Totz<johannes@jo-t.de> > > >> wrote: > > >> > > >> On 19/01/2012 16:26, Andreas Nilsson wrote: > > >>> > > >>> Hello, > > >>>> > > >>>> I'm trying to wrap my head around the process of booting from a > > >>>> zfs snapshot. I have hit a few roadblocks, which I hope this is > > >>>> the adequate list to post to regarding those. > > >>>> > > >>>> A short note on what I'm trying to achieve might be in order. In > > >>>> short: a > > >>>> nanobsd system on zfs only. I want to boot from a snapshot so > > >>>> that when I > > >>>> push out an upgrade with zfs send, I want the root filesystem to > > >>>> remain unchanged. > > >>>> > > >>>> The problems I've hit so far: > > >>>> *1 Making the zpool.cache file available > > >>>> *2 Having / mount via entry in fstab. > > >>>> > > >>>> > > >>> FWIW, I dont use any fstab for my zfs-only machine. Works > > >>> perfectly fine with mountpoint property. > > >>> > > >> > > >> > > >> It was just a small hope that the boot would continue with the > > >> filesystem pointed out by the bootfs property. I'm setting > > >> vfs.root.mountfrom in loader.conf now. > > >> > > >> > > >> > > >>> > > >>> *1: The zpool.cache is needed to autoimport a pool as I > > >>> understand it. Is > > >>> > > >>>> there a way to force the kernel to import a pool during bootup > > >>>> even though > > >>>> no zpool.cache is around? What does this file actually contain? > > >>>> > > >>>> I made an experiment and booted a disk with zfs root from > > >>>> machine a in machine b and that worked. I did partition the disk > > >>>> with gpart using a gpt > > >>>> scheme, and labeled the partition on which the pool resides as > > >>>> os, and upon > > >>>> creation of the zpool used gpt/os as device. Does this mean that > > >>>> as long as > > >>>> gpt/os is available, any machine boot this disk will have the > > >>>> zpool autoimported? > > >>>> > > >>>> > > >>> Not quite sure I understand you here. Just a note: booting kernel > > >>> and mounting root fs are two different things. the *zfsloader > > >>> will happily load > > >>> the kernel off a pool and boot it but mounting root might fail > > >>> later (I guess if no cachefile is present?). > > >>> > > >>> Sorry for being unclear. What I experience is exactly what you're > > >> describing: gptzfsloader loads the kernel and runs it just fine, > > >> but mounting root fails due to missing zpool.cache. > > >> > > >> I'm looking for a way to have the pool imported without the > > >> zpool.cache > > >> > > >> > > >> > > >>> > > >>> *2: Having a line like > > >>>> tank/root/8.2-RELEASE-p5@ro / zfs ro 0 0 > > >>>> in fstab causes mount to throw an error and leave me in single > > >>>> user mode, > > >>>> when the system is booted however mount can mount a zfs snapshot > > >>>> just fine. > > >>>> Setting vfs.root.mountfrom in loader.conf works just fine though. > > >>>> > > >>>> > > >>> The above I still think is rather strange: setting > > >>> vfs.root.mountfrom > > >> to a > > >> snapshot ( given that the snapshot has the zpool.cache file) > > >> works, but not > > >> having the corresponding line in fstab. > > >> > > >> > > >>> > > >>> -- > > >>> Sent from my<insert random gadget here> > > >>> > > >>> > > >> What I'm seeking a solution to is this: Boot several machines from > > >> one zfs snapshot. Since the stream from zfs send is also used to > > >> do the initial install there is no easy way to get the correct > > >> zpool.cache file in the snapshot. I guess one possible way to > > >> tackle this problem is to modify zpool so that all pools get > > >> created with the same id. > > >> > > > > > > There's a way to pre-load a zpool.cache via the loader (from an > > > alternative location). Can't remember the correct variables to set > > > right now... > > > > > > As for w/o any cache file... no idea. > > > > > > Ok, I'll research that. If it could be loaded from another > > > disk/partition > > I could really use it :) > > > > It is of course possible to edit the cachefile property of the > > zpool, but I think one can only set it to something relative the > > dataset from which one boots. > > > > Regards > > Andreas > > _______________________________________________ > > freebsd-fs@freebsd.org mailing list > > http://lists.freebsd.org/mailman/listinfo/freebsd-fs > > To unsubscribe, send any mail to "freebsd-fs-unsubscribe@freebsd.org" > > > Just a curious question: Will what you are trying to implement be > similar to Solaris boot environments/beadm? > Yes and no. I want my systems read-only, whereas solaris has root rw. And the bootenv is not really a snapshot, but a zfs clone of a snapshot ( ie writable ), which is not what I'm after. > > In short, Solaris boot environments are similar to what you described > (booting of snapshots) and are used to facilitate maintainance, > cf. > http://www.c0t0d0s0.org/archives/4372-New-features-of-Solaris-Alternate-boot-environments-based-on-snapshots.html > . > If so, maybe you can salvage code from there (or Illumos)? > > For general purpose fbsd setup, that is how I try to run the system. I actually did when I had fbsd on my laptop. I did start trying to port/implement it, which I thought would be easy since it is python-based, but I had more pressing issues so "doing it by hand" had to do. > Cheers, > -- > Christopher J. Ruwe > TZ GMT + 1 > > Cheers Andreas
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