Maybe I'm missing something, but why not create a software RAID 1+0 array of disks (easily doable with EBS volumes and mdadm) instead of relying on a heartbeat-

Maybe I'm missing something, but why not create a software RAID 1+0 array of disks (easily doable with EBS volumes and mdadm) instead of relying on a heartbeat-style solution as described in this post?