linux-ext4 - Re: [PATCH] default max mount count to unused

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Date:	Fri, 22 Jan 2010 11:40:41 -0700
From:	Andreas Dilger <adilger@....com>
To:	Ric Wheeler <rwheeler@...hat.com>
Cc:	Eric Sandeen <sandeen@...hat.com>, tytso@....edu,
	ext4 development <linux-ext4@...r.kernel.org>,
	Bill Nottingham <notting@...hat.com>
Subject: Re: [PATCH] default max mount count to unused

On 2010-01-22, at 10:02, Ric Wheeler wrote:
>> I've thought for quite a while that 20 mounts is too often, but I'm  
>> reluctant to turn it off completely.  I wouldn't object to  
>> increasing it to 60 or 80.
>>
>> At one time there was a patch that checked the state of the  
>> filesystem at mount time and only incremented only 1/5 of the time  
>> (randomly) if it was unmounted cleanly (not dirty, or not in  
>> recovery), but every time if it crashed.  The reasoning was that  
>> systems which crashed are more likely to have memory corruption or  
>> software bugs, and ones that shut down cleanly are less likely to  
>> have such problems.
>>
>
> I do like the snapshot idea, but also think that we need something  
> will not introduce random (potentially multi-hour or multi-day) fsck  
> runs after an otherwise clean reboot.
>
> If we hit this with a combination of:
>
> Reboot time:
>    (1) Try to mount the file system
>    (1) on mount failure, fsck the failed file system

Well, this is essentially what already happens with e2fsck today,  
though it correctly checks the filesystem for errors _first_, and  
_then_ mounts the filesystem.  Otherwise it isn't possible to fix the  
filesystem after mount, and mounting a filesystem with errors is a  
recipe for further corruption and/or a crash/reboot cycle.

> While up and running, do a periodic check with the snapshot trick.

Yes, this is intended to reset the periodic mount/time counter to  
avoid the non-error boot-time check.  If that is not running correctly  
then the periodic check would still be done as a fail-safe measure.

Cheers, Andreas
--
Andreas Dilger
Sr. Staff Engineer, Lustre Group
Sun Microsystems of Canada, Inc.

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