Thanks emmanuel and Celejar for your input.
actually i have been going through DRBD configurations and practicing, and i saw people mounting their DRBD drives to /etc/apache for apachi-failover and /somewhere/lib/mysql for mysql failover. i was just thinking why not i just mount DRBD drive on the root folder and tell apt-get install to copy all the files to specified path rather then default so i could avoid copying files from their installation directory to mount points then remount the mount point to their installation directory.
is it fine. though i am just practicing things are not in production. my production DRBD is working fine.