linux-ext4 - Re: mkfs.ext4 vs. e2fsck discard oddities

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Message-ID: <alpine.LFD.2.00.1203090957190.4487@dhcp-27-109.brq.redhat.com>
Date:	Fri, 9 Mar 2012 09:59:37 +0100 (CET)
From:	Lukas Czerner <lczerner@...hat.com>
To:	Phillip Susi <psusi@...ntu.com>
cc:	Lukas Czerner <lczerner@...hat.com>, "Ted Ts'o" <tytso@....edu>,
	Eric Sandeen <sandeen@...hat.com>,
	ext4 development <linux-ext4@...r.kernel.org>
Subject: Re: mkfs.ext4 vs. e2fsck discard oddities

On Thu, 8 Mar 2012, Phillip Susi wrote:

> On 3/1/2012 9:54 AM, Lukas Czerner wrote:
> > Well, it is not default right ? So the user should better know what is
> > he doing. Moreover it is not like it is end of the world when we do not
> > provide that option, since SSD's will handle over provisioning to some
> > extent even without slowdown, and as for thin-provisioned devices you
> > should know why you're overriding defaults and what it means for you.
> > 
> > Anyway, if people really want this another option to discard all the
> > block groups including those UNINIT ones, I guess I can not resist that
> > :). '-E discard_all' maybe ?
> 
> I think the option is a little more generic than discard.  The uninit groups
> are not discarded because they are not checked in the first place.  A bad
> group descriptor checksum will force the group to be checked, and thus
> discarded as well.  I think what is needed is an option to trigger the same
> thing: force all groups to be checked, even if they are uninit and have good
> descriptor checksums.  Maybe -E thorough?
> 

Why would we try to check UNINIT groups with valid descriptor checksums
? I think that this problem will be solved with BLOCK_DISCARDED flag as
we discussed with Ted in another thread. No need to have yet another
option so it is win-win :)

Thanks!
-Lukas
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