This assumes that you've at least created the correct partition for your DRBD already.
Notice that I am "diskless", that's because either your DRBD partition doesn't exist/has been renamed (eg. sdb becomes sda when sdb dies and you reboot) or because that drive is really actually dead/gone.
*If you need to permanently change the partition/device for your resource be sure to edit /etc/drbd.conf on both hosts and reload the config.
(replace r0 with........