Re: reiser4 plugins

Theodore Ts'o
2005-06-24T23:07:32Z

On Fri, Jun 24, 2005 at 12:21:18PM -0700, Hans Reiser wrote:
> There is an area where we suffered from writing fsck last. When there
> are two leaf nodes with the same key range AND the bitmap cannot be
> trusted to tell us which is the valid one, we don't know which is the
> most recent, and pick arbitrarily. Also, if you store a backup of V3,
> and you don't compress it, and you wipe out the bitmap blocks and need
> to use fsck, we don't know what blocks are backup image and what blocks
> are the fs. We advise users to never store a V3 backup on V3 without
> compressing it.

Unfortunately, there are plenty of reasons why you might want to store
a filesystem image on disk besides for backup purposes:

* Regression tests --- I have some 70+ small filesystem images
used for e2fsck's regression test suite. (I am always
amazed how many filesystem fsck programs don't have
regression test suites.)
* Initial ram-disk images
* Image files for qemu or user-mode-linux

... and probably many more. None of these are safe to store on a
reiserfs3 filesystem if you're worried about fsck being robust after a
disk failure.

Funny thing. When I tell system administrators who have been around
the block more than a few times about this particular "feature" of
reiserfs3, they usually very quickly decide that it's time to switch
to another filesystem.....

- Ted