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Re: XFS as Root filesystem

To: Klaus Strebel <stb@xxxxxxxxx>
Subject: Re: XFS as Root filesystem
From: "Stephen C. Tweedie" <sct@xxxxxxxxxx>
Date: Wed, 5 Apr 2000 14:30:50 +0100
Cc: Tan Pong Heng <pongheng@xxxxxxxxxxxxxx>, linux-xfs@xxxxxxxxxxx
In-reply-to: <38EB2FEA.E22A0E8B@ep-ag.com>; from stb@ep-ag.com on Wed, Apr 05, 2000 at 02:22:02PM +0200
References: <200004031359.IAA31585@jen.americas.sgi.com> <005601bf9dc0$64d9a4d0$a6e5a9ca@aries> <38EB2FEA.E22A0E8B@ep-ag.com>
Sender: owner-linux-xfs@xxxxxxxxxxx
Hi,

On Wed, Apr 05, 2000 at 02:22:02PM +0200, Klaus Strebel wrote:
> 
> the issue might be, that xfs has big problems, being mounted ro on boot.
> This is the same behaviour as on IRIX (i have a Origin 200 with IRIX 6.4
> on dksc(0,1,0) and IRIX 6.5 on dksc(0,2,0)). When i halt and reboot from
> the other OS's root, ex. 6.5, mounting ro of the 6.4 filesystems (esp.
> the root) on boot failes, due to dirty filesystem (on XFS impossible
> ;-). So the filesystems must 1. be mounted rw, umounted, and then
> mounted ro (what i wanted). Behaps, it helps, if you ensure, that lilo
> isn't booting with to ro-flag. Btw. ext3fs has the same problem. I think
> Steve Tweedie solved it in ext2-0.0.2d (didn't he, had no time to test).

All journaling filesystems need recovery.  It _can_ be possible to
build the appropriate recovery bits in memory if you have a readonly
boot, but most filesystems I'm aware of would want write access for
recovery after an unclean mount.

ext3 doesn't really "solve" this, but it does step around it: if you
mount a filesystem which needs recovery as readonly, then it will 
warn you that it is enabling write access to the device temporarily
and will perform the recovery.  The filesystem retains full ROFS
protection, but the device does get written to.  Ext3 does a device
check to make sure that the block device is writable before it 
attempts to do this, and if it is not, it will abort the mount
entirely: you can't mount ext3 on readonly media if recovery is 
needed.

--Stephen

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