Re: Linux-2.4.10 + ext3

Andrew Morton (
Sun, 23 Sep 2001 22:19:16 -0700

Aaron Lehmann wrote:
> ...
> I simply was hoping for insted of:
> <*> EXT2 fs
> <*> EXT3 fs
> (which is required today for most ext3-using people who want to do ext2
> mounts)
> ... there could be:
> <*> EXT2 fs
> <*> EXT3 journalling extensions
> AFAIK this would eliminate a lot of duplicate kernel code for ext3
> users.

mm.. The filesystems could be pretty much identical on the reading
path, but they're quite dissimilar on the writing path. So the
reading-stuff code could be commoned up.

I don't think it'd buy much, though. They are different filesystems
and the fact that ext3 borrows a lot of ext2 code is a useful
consequence of it having the same on-disk format.

And the main reason for having the same on-disk format is not, IMO, to
ease migration between the two filesystems. That's just a once-off
activity. The main reason for preserving compatibility is so that ext3
can leverage e2fsprogs, and the wealth of knowledge and understanding
of ext2 performance and behaviour.

The ext2-compatibility seems to be a bit of a political albatross
for ext3, really - people appear to be of the opinion that the
ext3 design was somehow compromised by the compatibility requirement.
This isn't so - ext3 is a block-level journalled filesystem. It
could have been based on minixfs, UFS, sysvfs, etc. Or it could
have been something altogether new. But I can't think of any benefit
in changing the on-disk format from its current ext2ness.

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