Following the announcement on lkml, I have started using ext3 on one of my
servers.  Since the server in question is a farily security-sensitive box, my
/usr partition is mounted read only except when I remount rw to install
packages.

I converted this partition to run ext3 with the mount options
"nodev,ro,data=writeback,defaults" figuring that when I need to install new
packages etc, that I could just mount rw as before and that metadata-only
journalling would be ok for this partition as it really sees very little write
activity.

When I try to remount it r/w I get a log message saying:
Jul 27 09:54:29 henry kernel: EXT3-fs: cannot change data mode on remount

...even if I give the full mount option list (including data=writeback) with
the remount instruction.

I can, however, remount it as ext2 read-write, but when I try to remount as
ext3 (even read only) I get the same problem.

Wierdly, "mount" lists it as being still an ext3 partition even though it has
been remounted as ext2.  I can't umount /usr because kjournald is currently
listed as using the partition.

The box in question is more-or-less RedHat 7.1, with ext3-2.4-0.9.4, kernel
2.4.7 and with the following relevant package versions:

mount-2.11g-4
util-linux-2.11f-3
e2fsprogs-1.22-2

...all from rawhide rpms.

I'm going to try one of the partitions mounted "data=ordered" to see if I see
the same sort of thing.

Sean