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SubjectRe: Ext3 Filesystem

On Mon, 6 Dec 1999 09:24:40 -0500 (EST), "Byron R. Stanoszek"
<> said:

> My thoughts on ext3:
> When looking into ext3, I thought it would be a completely different file
> system apart from ext2. However, I was surprised to see that most of
> the filesystem is the same except for using that journal.dat file. So I was
> wondering, couldn't this journaling filesystem really just be a flag added
> to one of the reserve bits in the ext2 header that labels it as such?

The filesystem internals have to be substantially changed for
journaling, but the on-disk filesystem *is* just marked by a flag in
the ext2 superblock which indicates that there is a journal present.
You can thus migrate between ext2 and ext3 on disk easily, but you
cannot use the same kernel code to mount ext2 and ext3.

> Also, I've read recently about the problems with root seeing
> journal.dat ... I feel the file shouldn't actually be part of the
> directory hierarchy, but stored within an normally-unaccessible
> portion of the ext2 partition.

The final release will have the journal in a hidden inode.

> From my point of view, I don't see it anything more than being an
> extension of ext2, and I figure once the design is finalized there
> would be options to some e2fs-tools programs to add journaling
> support to an already-existing ext2 filesystem, etc.

There already is. You can also remove journaling from an ext3


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