In the last time I get a lot questions and feedback to some older posts (Active/Passive Cluster) where I used DRBD. And actually I never wrote how to setup DRBD and I try to fill this gap now. Also this post will be a new ground for some new ideas and posts related to Active/Passive Clustering with KVM.
DRBD (Distributed Replicated Block Device) is a really cool cluster solution to have radundant data on two or more nodes. Everybody know RAID, DRBD is like RAID 1 over network.