Unfortunately, it is not possible to do either one.

Once you create `/dev/drbd0` on both DB Servers, you have to mount the DRBD Primary on a folder. That folder cannot have anything with active file handles. The protocol I use is:

    drbdadm primary drbd0
    mount /dev/drbd0 /var/lib/mysql
    service mysql start

You want DRBD to house MySQL Data. Here is what you must do instead

    service mysql stop
    mv /var/lib/mysql /var/lib/mysql_old
    mkdir /var/lib/mysql
    chown mysql:mysql /var/lib/mysql
    drbdadm primary drbd0
    mount /dev/drbd0 /var/lib/mysql
    cp -R /var/lib/mysql_old /var/lib/mysql
    chown -R mysql:mysql /var/lib/mysql
    service mysql start

As shown, stopping mysqld is mandatory.