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Re: XFS filesystem corruption

To: stan@xxxxxxxxxxxxxxxxx
Subject: Re: XFS filesystem corruption
From: Julien FERRERO <jferrero06@xxxxxxxxx>
Date: Fri, 8 Mar 2013 11:17:42 +0100
Cc: Ric Wheeler <rwheeler@xxxxxxxxxx>, Emmanuel Florac <eflorac@xxxxxxxxxxxxxx>, xfs@xxxxxxxxxxx
Delivered-to: xfs@xxxxxxxxxxx
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> Something that none of us mentioned WRT write barriers is that while the
> filesystem structure may avoid corruption when the power is cut, files
> may still be corrupted, in conditions such as any/all of these:
>
> 1.  unwritten data still in buffer cache
> 2.  drive caches are enabled
> 3.  BBWC not working properly
>
> If the techs are determined to hard cut power because they don't have
> the time or the knowledge to do a clean shutdown, it may be well worth
> your time/effort to write a script and teach the field techs to execute
> it, before flipping the master switch.  Your simple script would run as
> root, or you'd need to do some sudo foo within, and would contain
> something like:
>
> #! /bin/sh
> sync
> echo 2 > /proc/sys/vm/drop_caches
> echo "Ready for power down."
>
> This will flush pending writes in buffer cache to disk, and assumes of
> course that drive caches are disabled, and/or that BBWC, if present, is
> functioning properly.  It also assumes no applications are still
> actively writing files, in which case you're screwed regardless.  It's
> not a perfect solution and there's no guarantee you won't suffer file
> corruption, but this greatly increases your odds against it.

Thank you, that's the plan indeed. Educating our customer, and
minimize failure with such script / recommendation.

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