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Re: Corrupt XFS -Filesystems on new Hardware and Kernel

To: Jan Kara <jack@xxxxxxx>
Subject: Re: Corrupt XFS -Filesystems on new Hardware and Kernel
From: Jens Axboe <jens.axboe@xxxxxxxxxx>
Date: Thu, 29 Mar 2007 13:14:07 +0200
Cc: Linda Walsh <lkml@xxxxxxxxx>, Oliver Joa <oliver@xxxxxxxx>, Eric Sandeen <sandeen@xxxxxxxxxxx>, David Chinner <dgc@xxxxxxx>, linux-kernel@xxxxxxxxxxxxxxx, xfs-oss <xfs@xxxxxxxxxxx>
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On Thu, Mar 29 2007, Jan Kara wrote:
> > Oliver Joa wrote:
> > >>eason or another, xfs has detected a corrupted on-disk inode format 
> > >>which it cannot recognize, and shuts down.
> > ----
> > Oh, one other thing that may not apply in your case, but may.
> > Does your SATA disk support write caching?  Does it support
> > something called a barrier function?  (not real clear on all
> > the ways this can go wrong, but I believe barriers are supposed
> > to guarantee previous data has been fixed on disk (not in write
> > cache).  If the SATA controller issues a reset, it may very well
> > purge the write cache.  Theoretically, I can think of a _possibility_,
> > that the reset disk would purge the write cache and the barrier
> > indicator would tell xfs to resume writing.  From a recent thread
> > on the xfs list, it would appear this could be a "bad" thing (like
> > crossing the streams ala "ghostbusters", but in a data-integrity
> > context).
>   As far as I can remember, barrier does not mean that data is fixed on
> disk. It is only a command that forces all the writes before the barrier
> to be performed before all the writes after the barrier. So this is more
> an ordering restriction than a data integrity thing...

A barrier write guarentees both data before barrier is on disk, as well
as the barrier itself when completion is signalled.

Jens Axboe

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