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

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Date:	Fri, 22 Oct 2010 07:30:46 -0400
From:	Ric Wheeler <ricwheeler@...il.com>
To:	Lukas Czerner <lczerner@...hat.com>
CC:	Andreas Dilger <adilger.kernel@...ger.ca>,
	linux-ext4@...r.kernel.org, tytso@....edu, sandeen@...hat.com
Subject: Re: [PATCH] e2fsck: Discard free data and inode blocks.

  On 10/22/2010 05:12 AM, Lukas Czerner wrote:
> On Thu, 21 Oct 2010, Andreas Dilger wrote:
>
>> On 2010-10-21, at 08:15, Lukas Czerner wrote:
>>> In Pass 5 when we are checking block and inode bitmaps we have great
>>> opportunity to discard free space and unused inodes on the device,
>>> because bitmaps has just been verified as valid. This commit takes
>>> advantage of this opportunity and discards both, all free space and
>>> unused inodes.
>>>
>>> I have added new option '-K' which when set, disables discard. Also when
>>> the underlying device does not support discard, or BLKDISCARD ioctl
>>> returns any kind of error, or when some errors occurred in bitmaps, the
>>> discard is disabled.
>> I'm always a bit nervous with patches like this, that will prevent data recovery after an e2fsck run (which seems like the opposite of what we want from e2fsck).
>>
>> Two suggestions:
>> - it probably makes sense to disable this by default, and allow it to be
>>    specified on the command-line and e2fsck.conf
>> - should we really have a short option, or a "-E discard" and "-E nodiscard"
>>    options, which allow us to change the default easily at some later time
>>    (which we can't do with a single -K flag)
> Right, I agree it would be probably better to disable this by default.
>
>

If we do disable it by default, I think that we might also want to be consistent 
and disable the discard support in mkfs by default as well?

thanks!

Ric

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