As briefly mentioned in Pacemaker Explained, DRBD devices need two different values set for their monitor intervals:
ocf:linbit:drbd \ params drbd_resource="
" \ op monitor interval="61s" role="Slave" \ op monitor interval="59s" role="Master"
The reason is that Pacemaker distinguishes monitor operations by their resource and their interval – but not by their role. So, if this distinction is not done “manually”, Pacemaker will monitor only one of the two (and, with DRBD 9, more) nodes, which is not what you want (usually).