linux-ext4 - Re: breaking ext4 to test recovery

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Message-ID: <AANLkTinJ4-PPTi0q76fThmq9a_qe1PadVueObPtRLruY@mail.gmail.com>
Date:	Tue, 29 Mar 2011 13:33:51 -0400
From:	Greg Freemyer <greg.freemyer@...il.com>
To:	Rogier Wolff <R.E.Wolff@...wizard.nl>
Cc:	Eric Sandeen <sandeen@...hat.com>,
	Daniel Taylor <Daniel.Taylor@....com>,
	linux-ext4@...r.kernel.org
Subject: Re: breaking ext4 to test recovery

On Tue, Mar 29, 2011 at 10:33 AM, Rogier Wolff <R.E.Wolff@...wizard.nl> wrote:
> On Tue, Mar 29, 2011 at 08:50:18AM -0500, Eric Sandeen wrote:
>> Another tool which can be useful for this sort of thing is
>> fsfuzzer.  It writes garbage; using dd to write zeros actually
>> might be "nice" corruption.
>
> Besides writing blocks of "random data", you could write blocks with a
> small percentage of bits (byte) set to non-zero, or just toggle a
> configurable number of bits (bytes). This is slightly more devious than just
> "random data".

I don't know what exactly is being tested, but "hdparm
--make-bad-sector" can be used to create a media error on a specific
sector.

Thus allowing you to simulate a sector failing in the middle of the journal.

I assume that is a relevant test.

fyi: --repair-sector undoes the damage.  You may need to follow that
with a normal write to put legit data there.

If you try a normal data write without first repairing, the drive
should mark the sector permanently bad and remap that sector to a
spare sector.

I have only used these tools with raw drives, no partitions, etc.  So
I've never had to worry about data loss, etc.

Greg
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