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Re: xfs_force_shutdown after Raid crash

To: Michael Monnerie <michael.monnerie@xxxxxxxxxxxxxxxxxxx>
Subject: Re: xfs_force_shutdown after Raid crash
From: Dave Chinner <david@xxxxxxxxxxxxx>
Date: Thu, 5 Feb 2009 19:37:00 +1100
Cc: xfs@xxxxxxxxxxx
In-reply-to: <200902041624.32354@xxxxxx>
Mail-followup-to: Michael Monnerie <michael.monnerie@xxxxxxxxxxxxxxxxxxx>, xfs@xxxxxxxxxxx
References: <498376CF.8020806@xxxxxxxxxxxxxx> <200902040952.45440@xxxxxx> <20090204122241.GL24173@disturbed> <200902041624.32354@xxxxxx>
User-agent: Mutt/1.5.18 (2008-05-17)
On Wed, Feb 04, 2009 at 04:24:27PM +0100, Michael Monnerie wrote:
> (compressing 2 answers here)
> 
> On Mittwoch 04 Februar 2009 Dave Chinner wrote:
> > > With a single hard disk and barriers turned on (on=default), a
> > > powerfail "only" looses data in the cache but at least does not
> > > destroy the filesystem.
> >
> > I'd drop this paragraph - powerfail can destroy filesystems even on
> > a single disk (e.g. root directory gets corrupted).
> 
> Isn't that what barriers are for? If I understand correctly, barriers 
> help against destroying the filesys, except root dir? But that should 
> "easily" be fixable with xfs_repair or so?

See, I didn't understand what you were trying to say. ;)

What I missed was the "barriers turned on" - I was referring
(context not quoted) to the fact that RAID5 is not unіque in it's
ability to trash the filesystem on powerfail. You are right,
barriers on a single disk should prevent filesystem corruption
and will prevent loss of synchronously written data. only
asynchronously written data will get lost (just like all the
stuff sitting in RAM).

Cheers,

Dave.
-- 
Dave Chinner
david@xxxxxxxxxxxxx

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