Date: Mon, 23 Jan 2012 05:58:49 -0800 From: Jeremy Chadwick <freebsd@jdc.parodius.com> To: Andreas Nilsson <andrnils@gmail.com> Cc: freebsd-fs@freebsd.org, Johannes Totz <johannes@jo-t.de> Subject: Re: Booting from zfs snapshot Message-ID: <20120123135849.GA84966@icarus.home.lan> In-Reply-To: <CAPS9%2BSvA8c=uY7b%2BeKMrA2CnFS4Kg1ccxgaVYm9RSZy1GQ6ChA@mail.gmail.com> 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>
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On Mon, Jan 23, 2012 at 02:42:19PM +0100, Andreas Nilsson 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. I believe this is what you're looking for: http://lists.freebsd.org/pipermail/freebsd-fs/2011-May/011556.html -- | Jeremy Chadwick jdc@parodius.com | | Parodius Networking http://www.parodius.com/ | | UNIX Systems Administrator Mountain View, CA, US | | Making life hard for others since 1977. PGP 4BD6C0CB |
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