> lower device(/dev/hda6) is already mounted
> I can't do any change to the partition nor do I move the directories.

If you can't change partitioning, and (as I presume this implies) don't have a spare empty partition available to use as the physical partition ("lower device") for DRBD, you won't get very far - don't mirror the entire /var between the two machines!

Can you add a second disk to the Untouchable machine for /var/www alone?

OTOH - I know this is the DRBD list, but if the above really cannot be changed, wouldn't you be better off running rsync in a cron job???  I mean, how often is the data on your /var/www going to be updated, and do you need up-to-the second recovery?  You can still use heartbeat to make the web service HA ...

--Peter