linux-ext4 - Re: [PATCH] e2fsck: Discard free data and inode blocks.

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Date:	Fri, 22 Oct 2010 13:27:19 -0500
From:	Eric Sandeen <sandeen@...hat.com>
To:	Andreas Dilger <adilger.kernel@...ger.ca>
CC:	Lukas Czerner <lczerner@...hat.com>,
	Ric Wheeler <ricwheeler@...il.com>, linux-ext4@...r.kernel.org,
	tytso@....edu
Subject: Re: [PATCH] e2fsck: Discard free data and inode blocks.

Andreas Dilger wrote:
> On 2010-10-22, at 08:32, Lukas Czerner wrote:
>>>> There is a concern that discard might prevent data recovery
>>>> after fsck because it might be already discarded (some weird fs
>>>> corruption?) in pass 5. However in my opinion this is a very
>>>> small window (if there even is any), because we have already
>>>> passed check 1-4 and we have just confirmed that group
>>>> descriptors should be ok.
> 
> I don't totally agree.  When users have a serious filesystem problem,
> the first thing they normally do is run e2fsck to see if it is
> corrected (it may even be done automatically at boot after
> errors=panic causing a reboot.
> 
> After that, they may want to recover some more data (e.g. with
> ext3grep, or restore an e2image of the metadata, and re-run e2fsck).
> If e2fsck will discard all of the data then any data recovery will be
> impossible.

Could set it to only issue discard when the check was clean....

It could still be an option of course, but that might be safer still.

-Eric
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