Date: Mon, 23 Jan 2012 12:58:34 +0000 From: Johannes Totz <johannes@jo-t.de> To: freebsd-fs@freebsd.org Subject: Re: Booting from zfs snapshot Message-ID: <jfjlhq$p77$1@dough.gmane.org> In-Reply-To: <CAPS9%2BSvtYZt1m26jCqRH6c3w_aB3hWt56ZFoYJAw_cEu2NANzg@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>
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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.
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