Re: Placing the root partition on an XFS filesystem is not supported

From: Dave Chinner <david@fromorbit.com>
To: Eric Sandeen <sandeen@sandeen.net>
Cc: linux-xfs@oss.sgi.com, Marcos Mello <marcosfrm@gmail.com>
Subject: Re: Placing the root partition on an XFS filesystem is not supported
Date: Mon, 6 Feb 2012 12:54:30 +1100	[thread overview]
Message-ID: <20120206015430.GK6922@dastard> (raw)
In-Reply-To: <4F2F1B28.3060308@sandeen.net>

On Sun, Feb 05, 2012 at 06:13:28PM -0600, Eric Sandeen wrote:
> On 2/5/12 6:11 PM, Dave Chinner wrote:
> > On Fri, Feb 03, 2012 at 12:50:17PM -0600, Eric Sandeen wrote:
> >> On 2/3/12 8:39 AM, Marcos Mello wrote:
> >>> Eric Sandeen <sandeen <at> sandeen.net> writes:
> >>>
> >>>>
> >>>> In general there is no problem with xfs on a root partition.  However, the
> >>> installer
> >>>> may not make it easy or available for you.
> >>>>
> >>>> (I never use xfs for /boot though, I don't trust grub enough for that
> >>> honestly).
> >>>>
> >>>> -Eric
> >>>
> >>> Same thing on Fedora 16. Let's hope some day Anaconda will change that.
> >>
> >> F16 prevents it?  I didn't see it in the upstream tree.  That should
> >> not be so.  :/
> >>
> >>> About GRUB with a XFS /boot the problem was with GRUB Lagacy, wasn't it?
> >>> Or GRUB2 is still buggy?
> >>
> >> I have no idea, actually.  I delved into grub a bit, it was disturbing
> >> enough that I have not tried to look at grub2.  :)
> > 
> > Certainly the problem exists with legacy grub - it assumes that it
> > can write to the first sector or any disk or partition which
> > overwrites the XFS superblock...
> 
> well, it was worse than that.  I can work around the grub-on-a-partition
> problem, but what I ran into was grub reading & writing to/from the block
> device under a mounted filesystem - corruption and hilarity ensued.

Oh, grub2 does worse things than that - grub_probe mounts any device
that appears to have a valid superblock so it can find out what
devices it needs to list in it's boot menu. I found this out when I
built a big DM stripe out of disks that used to have filesystems on
them.  grub-probe mounted every single device -inside- the stripe
and ran log recovery on them, corrupting the new filesystem and
quite a bit of data on the DM stripe they were part of....

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com

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