"In this procedure, you have learned how to set up a
DRBD device on a SAN network. That's a nice start if you want to
create a mission-critical open source SAN, but it's not good
enough. As your servers are configured right now, if san1 goes
down, you need to issue the drbdsetup primary command manually on
the second server, which you don't want to do. That is where
Heartbeat cluster comes in. And in the next part of this series,
we'll discuss how to set up this cluster."