linux-ext4 - Re: Ext3 behavior on power failure

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Message-ID: <20070328150003.GE29587@duck.suse.cz>
Date:	Wed, 28 Mar 2007 17:00:03 +0200
From:	Jan Kara <jack@...e.cz>
To:	armangau_philippe@....com
Cc:	jakj@...-k-j.com, jack@...e.cz, ric@...imap.lss.emc.com,
	ext3-users@...hat.com, linux-ext4@...r.kernel.org,
	csar@...nford.edu
Subject: Re: Ext3 behavior on power failure

On Wed 28-03-07 10:17:33, armangau_philippe@....com wrote:
> In my case the disk cache is not a  problem - We use an emc disk array
> the write cache is protected - 
> Once the data has made over the disk array we can assume it is safe - 
  Then if you are able to reproduce the situation that not all data
is written after fsync(); poweroff; that is a bug worth reporting..

								Honza
> 
> -----Original Message-----
> From: John Anthony Kazos Jr. [mailto:jakj@...-k-j.com] 
> Sent: Wednesday, March 28, 2007 9:17 AM
> To: Jan Kara
> Cc: wheeler, richard; armangau, philippe; ext3-users@...hat.com;
> linux-ext4@...r.kernel.org; csar@...nford.edu
> Subject: Re: Ext3 behavior on power failure
> 
> >  If you fsync() your data, you are guaranteed that also your data are
> > safely on disk when fsync returns. So what is the question here?
> 
> Pardon a newbie's intrusion, but I do know this isn't true. There is a 
> window of possible loss because of the multitude of layers of caching, 
> especially within the drive itself. Unless there is a
> super_duper_fsync() 
> that is able to actually poll the hardware and get a confirmation that
> the 
> internal buffers are purged?
> 
-- 
Jan Kara <jack@...e.cz>
SuSE CR Labs
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