Date: Wed, 2 May 2012 15:28:11 +1000 From: Peter Jeremy <peterjeremy@acm.org> To: Matthew Seaman <matthew@FreeBSD.org> Cc: freebsd-fs@FreeBSD.org Subject: Re: ZFS with multiple boot/root pools Message-ID: <20120502052811.GA71211@server.vk2pj.dyndns.org> In-Reply-To: <4F9F8888.3030104@FreeBSD.org> References: <20120430210711.GA50280@server.vk2pj.dyndns.org> <4F9F8888.3030104@FreeBSD.org>
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On 2012-May-01 07:54:00 +0100, Matthew Seaman <matthew@FreeBSD.org> wrote:
>On 30/04/2012 22:07, Peter Jeremy wrote:
>> Can anyone suggest a way to configure a zpool or set of filesystems
>> so that they will only be mounted if the root filesystem is within
>> the zpool.
>
>Not exactly that, but this should suffice.
It sounds good but I can't make it work.
>Suppose your two pools are zpool1 and zpool2. You have several ZFSes on
>each pool, all of which should be set to the default[*] that they are
>all mounted relative to the top level ZFS -- either zpool1/ or zpool2/
>-- so to avoid overlaps, all you need to do is mount the top level ZFS
>at a unique path.
Yep. To go further, assume there are also zpool{1,2}/var filesystems,
one of which should be mounted as /var. The mountpoint for zpool{1,2}/var
can be one of:
A) legacy
This requires an entry in each /etc/fstab for /var
B) inherited
This depends on the value of mountpoint for zpool{1,2}:
a) legacy
Same as (A) above.
b) inherited
The mountpoint will be set to /zpool{1,2}/var
c) Set to some arbitrary value, say /foo
The mountpoint will be set to /foo/var
C) /var
This results is two /var filesystems unless one is marked "canmount=3Dno=
auto"
>One way of doing this is to set the mountpoints for the top level
>zpool1/ and zpool2/ to legacy, and create /etc/fstab in each pool like so:
>
>in zpool1/
>
>zpool1 / zfs rw 0 0
>zpool2 /ROOT/zpool2 zfs rw 0 0
Following the breakdown above, this implies I'd also need an entry in
/etc/fstab:
zpool1/var /var zfs rw 0 0
>Another way of doing this is to realise that the vfs.root.mountfrom
>property in /boot/loader.conf overrides any internal settings in the
>zpools. This means that you can set the mountpoint for zpool1/ and
>zpool2/ to some distinct values, say, /ROOT/zpool1 and /ROOT/zpool2
Whilst this overrides the mountpoint for the root filesystem, it has
no effect on other filesystems in the pool. In particular, the
mountpoint for zpool1/var remains /zpool1/var and the "zfs mount -a"
fails because there's no /zpool1
>If vfs.root.mountfrom is set to zfs:zpool1 then that zpool will be
>mounted as the root filesystem at / and zpool1/usr, zpool1/var etc. etc.
>will all be mounted in the expected locations relative to that.
Unfortunately my experiments on a 10-current box show this doesn't
happen. Inheriting a mountpoint means that the filesystem's
mountpoint is set to the parent's nominal mountpoint (ie zpool{1,2}),
not the actual mountpoint (ie /), with the filesystem name appended.
>Apart from the wrinkle of having two different zpools, this is
>essentially how ZFS boot environments work.
Except that beadm/manageBE does a lot of other juggling to switch
between BEs.
>http://www.infracaninophile.co.uk/articles/install-on-zfs/ but there are
>several other treatments around.
I've had a look through those notes and you are still specifying
mountpoints for (eg) zroot/ROOT/9.0-RELEASE/usr - which implies you
wind up with multiple /usr's mounted. =20
--=20
Peter Jeremy
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