linux-ext4 - Re: [RFC] [PATCH] Flex_BG ialloc awareness V2.

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Date:	Fri, 14 Dec 2007 12:07:23 -0600
From:	"Jose R. Santos" <jrs@...ibm.com>
To:	Andreas Dilger <adilger@....com>
Cc:	linux-ext4 <linux-ext4@...r.kernel.org>
Subject: Re: [RFC] [PATCH] Flex_BG ialloc awareness V2.

On Fri, 14 Dec 2007 10:01:06 -0700
Andreas Dilger <adilger@....com> wrote:
> Well, I can imagine in some cases that the flexbg will not be completely
> contiguous on disk (e.g. after a filesystem resize, if there are bad
> blocks, etc).  As long as the group descriptors themselves are correct
> (i.e. referencing valid bitmaps/itable) then it shouldn't cause a mount
> failure if the per-group data isn't strictly aligned according to the
> superblock flexbg count.

Yes, the meta-data may not be completely contiguous on the disk as per
the definition of flexbg.  What I was planing on doing was to check the
first, second and last-1 flexbg to see if how the meta-data is
arranged.  If none of those flexbg matches the size of the flexbg size
in the super block the we can set sbi->s_groups_per_flex_shift to zero
which would make the fs fallback to Orlov.

> We would need to validate the group descriptor separately though (e.g.
> group checksums).

Agree

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

-JRS
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