Normally when you have shared storage, you can use that shared storage as a quorum device (i.e., via an exclusive scsi lock). If you have something like DRBD,

Normally when you have shared storage, you can use that shared storage as a quorum device (i.e., via an exclusive scsi lock). If you have something like DRBD, then you still have the issue where each node can't see each other, but an outside application writing to the database served up by the cluster can see both nodes -- and if each node wants to bring up it's shared IP address, some writes will go to one node, some to the other. Then you have the database on each node not having all the current data (even if it isn't technically "corrupted").