linux-ext4 - Re: breaking ext4 to test recovery

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Message-ID: <alpine.LFD.2.00.1104011724140.3151@dhcp-27-109.brq.redhat.com>
Date:	Fri, 1 Apr 2011 17:26:16 +0200 (CEST)
From:	Lukas Czerner <lczerner@...hat.com>
To:	Eric Sandeen <sandeen@...hat.com>
cc:	Andreas Dilger <adilger@...ger.ca>,
	Daniel Taylor <Daniel.Taylor@....com>,
	linux-ext4@...r.kernel.org
Subject: Re: breaking ext4 to test recovery

On Thu, 31 Mar 2011, Eric Sandeen wrote:

> On 3/31/11 5:21 PM, Andreas Dilger wrote:
> 
> > We have a kernel patch "dev_read_only" that we use with Lustre to
> > disable writes to the block device while the device is in use.  This
> > allows simulating crashes at arbitrary points in the code or test
> > scripts.  It was based on Andrew Morton's test harness that he used
> > for ext3 recovery testing back when it was being ported to the 2.4
> > kernel.
> > 
> > http://git.whamcloud.com/?p=fs/lustre-release.git;a=blob_plain;f=lustre/kernel_patches/patches/dev_read_only-2.6.32-rhel6.patch;hb=HEAD
> >
> >  The best part of this patch is that it works with any block device,
> > can simulate power failure w/o any need for automated power control,
> > and once the block device is unused (all buffers and references
> > dropped) it can be re-activated safely.
> 
> It won't simulate a lost write cache though, will it?

That's a very good question, I would like to know if there is any way at
all to force the device to drop the write cache. That would really help
the power failure testing filesystems.

-Lukas

> 
> -Eric
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