Some time ago I created a High Availability iSCSI target using Ubuntu Linux, iscsi-target, DRBD and heartbeat. The HA cluster consisted of two nodes and the iSCSI initiators were Windows Server 2008. I was able to mount the LUN and copy a video to it, play it back and then pull the power from the primary iSCSI target. A few seconds later the second iSCSI target took over and video continued to play.
Pretty cool, huh?
Here is my guide if you want to try this. Although I've not gone back through the guide to make sure it's correct. But if you spot anything that's wrong or not very clear, please leave a comment.