Changing the entire question as earlier one was very confusing.

I have been exploring different clustering system to run Virtual machines on two different machines on LAN with high availability.

Currently I am already using DRBD resource on two different machines on Primary/Secondary mode. In case the primary fails I manually promote the secondary to Primary and start the VM.

I also explored Gluster and looks good, however, I would rather prefer clustering over Gluster (user space FS).

So if anyone has idea which one would be better from ease of use prospective please I would be interested in.

Moreover, sheepdog project appears good, however, could not find much documentations/Howtos.

I am using Centos 6.