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Re: XFS as Root filesystem

To: "Stephen C. Tweedie" <sct@xxxxxxxxxx>
Subject: Re: XFS as Root filesystem
From: Steve Lord <lord@xxxxxxx>
Date: Wed, 05 Apr 2000 09:40:37 -0500
Cc: Klaus Strebel <stb@xxxxxxxxx>, Tan Pong Heng <pongheng@xxxxxxxxxxxxxx>, linux-xfs@xxxxxxxxxxx
In-reply-to: Message from "Stephen C. Tweedie" <sct@xxxxxxxxxx> of "Wed, 05 Apr 2000 14:30:50 BST." <20000405143050.I9399@xxxxxxxxxx>
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

Just to report on where XFS is in all of this, it will fail a read only
mount request if it determines recovery needs to be run. We do have
a norecovery mount option - but this is really for internal use only,
I would not recommend using it.

Stephen's idea looks interesting, I will dig into it for XFS.

Steve (really Stephen, but that gets confusing on Linux related topics!)

------------------------------------------------------------------------------
Steve Lord                                      voice: +1-651-683-5291
Silicon Graphics Inc
655F Lone Oak Drive                             email: lord@xxxxxxx
Eagan, MN, 55121, USA
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