Ext3 users - Oct 2001 - How safe is journalling?

Sorry if this message has been posted by someone else before, but I
couldn't find anything similar in the last couple of months of archive.

The question is how safe is journalling, in general? The "ordered"
mount
option for ext3 seems pretty safe, but is it possible that if the drive's
power went half way through writing to the journal, could it be left in an
inconsistent state? I mean, is writing to the journal an "atomic"
process?

Sorry if this is a stupid question...!

Jeremy

-- 
Jeremy Sanders <jss@ast.cam.ac.uk>  http://www-xray.ast.cam.ac.uk/~jss/
Pembroke College, Cambridge. UK   Institute of Astronomy, Cambridge. UK

On Oct 31, 2001  17:42 +0000, Jeremy Sanders wrote:
> The question is how safe is journalling, in general? The
"ordered" mount
> option for ext3 seems pretty safe, but is it possible that if the
drive's
> power went half way through writing to the journal, could it be left in an
> inconsistent state? I mean, is writing to the journal an "atomic"
process?
This is the whole point of having a journaled filesystem.  The journal
is only really useful when your system fails.  Otherwise, it is just
overhead for 99% of uses.

The journal guarantees that the filesystem metadata is always consistent
after a crash.  You may lose some operations from just before the crash,
but you probably would have anyways (probably not quite as many as with
a journal), because of buffering.

Cheers, Andreas
--
Andreas Dilger
http://sourceforge.net/projects/ext2resize/
http://www-mddsp.enel.ucalgary.ca/People/adilger/