On Mon, Oct 23, 2006 at 05:35:02AM +0000, Michael van Elst wrote:
> wrstuden@NetBSD.org (Bill Studenmund) writes:
> 
> >Why? If you are up-to-date enough to have a journaled file system, why=20
> >don't you have up-to-date tools?
> 
> You may need to transport the disk to an older system and you
> may want to run the same filesystem without journaling.
> 
> This is not a necessary feature, it is just nice to have. With
> ext3 I can promote/demote from/to ext2 easily. With Solaris UFS
> the journal ist just a mount option.
> 
> >Old tools don't know how to tell if a journal is dirty.
> 
> True, the journal would be lost.

ext3 does not have this problem. Old tools know if the journal is dirty,
refuse to work if it, and work correctly if it is clean.

Maybe FFS could imitate this by writing an incompatible magic number to the
superblock if journalling is in action, and when the filesystem is cleanly
unmounted, replace it with the old magic number.

Pavel