This is more boring parts but you must lay a good foundation.
All the resources must be in place before you configure
Pacemaker. The default location for MySQL data is /var/lib/mysql.
You will be moving this to the DRBD file system in
/data/mysql. The default MySQL configuration is in
/etc/my.cnf. I move it to /data/mysql so updates will move
with system fail overs. To keep life simple I use
sym-links to point from /var/lib/mysql and /etc/my.cnf to their
Install MySQL of your choise on DB1, DB2 and DB3.