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Re: XFS as Root filesystem

To: Lyle Seaman <lws@xxxxxxxxxxxxxxxx>
Subject: Re: XFS as Root filesystem
From: "Stephen C. Tweedie" <sct@xxxxxxxxxx>
Date: Thu, 6 Apr 2000 16:21:44 +0100
Cc: linux-xfs@xxxxxxxxxxx, Stephen Tweedie <sct@xxxxxxxxxx>
In-reply-to: <38EB8FEF.9CB411C@xxxxxxxxxxxxxxxx>; from lws@xxxxxxxxxxxxxxxx on Wed, Apr 05, 2000 at 03:11:44PM -0400
References: <200004051440.JAA25697@xxxxxxxxxxxxxxxxxxxx> <38EB8FEF.9CB411C@xxxxxxxxxxxxxxxx>
Sender: owner-linux-xfs@xxxxxxxxxxx
Hi,

On Wed, Apr 05, 2000 at 03:11:44PM -0400, Lyle Seaman wrote:
> 
> How does a readonly filesystem become inconsistent?
> (esp: "how does ext3 on readonly media" become inconsistent?)
> 
> The obvious answer is "well, it *wasn't* readonly when it
> became inconsistent".
> 
> If that's the case, then why do you care?  Naively, I wouldn't
> think this is a big deal.  Why am I wrong?

Because (a) existing Linux installations expect to mount the
root filesystem readonly until basic consistency checking has
been done; and (b) after a cold reboot, the filesystem will 
need recovery before it can be mounted.

In practice there is no problem mounting the root filesystem
read-write if you have journaling, with one important exception:
if you detect actual errors on the fs such that a constency 
check is required, mounting the fs read-write is dangerous.
(Ext2/ext3 mark an error flag in the superblock if they detect
dangerous inconsistencies in the fs so that a subsequent fsck
will be forced.  I don't know if xfs does this or not.)

--Stephen

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