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Re: ext3 external journal and fstab



On Sun, Dec 29, 2002 at 10:00:52PM +0100, Norman Schmidt wrote:
> Hi again!
> 
> I would like to add an ext3 partition (eg. /dev/md11) with its external 
> journal (on /dev/md21) to /etc/fstab in order to have it mounted while 
> system-startup.
> 
> Do I have to specify the external journal device in fstab or does the 
> partition find its journal device by itself? If the first, ho should I 
> specify it?

The system should be able to find the journal device by itself.  The
device number is encoded in the superblock, which is what it currently
uses.  What it *should* happen is that the userspace tools (i.e.,
should look up the journal UUID in the superblock, and search for the
journal using the device number in the superblock as a hint, but
searching the devices in /proc/partitions looking for a journal with
the current UUID, and then pass this information to the kernel).  This
way, the external journal can be found even if the device number
changes.

There's a bunch of polishing work with using external journals that
still needs to be done in order so that using them is bulletproof.
Right now, if the system administror reconfigures their md devices,
then the kernel won't be able to find the external journal, and they
will get a confusing error message.  That's rather unfortunate.

						- Ted





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