[CentOS] best practices in using shared storage for XEN Virtual Machines and auto-failover?

Hi all,

Can anyone pleas tell me what would be best practice to use shared storage with virtual machines, especially when it involved high availability / automated failover between 2 XEN servers?

i.e. if I setup 2x identical XEN servers, each with say 16GB RAM, 4x 1GB NIC's, etc. Then I need the xen domU's to auto failover between the 2 servers if either goes down (hardware failure / overload / kernel updates / etc).

What is the best way to connect a NAS / SAN to these 2 servers for this kind of setup to work flawlessly? The NAS can export iSCSI, NFS, SMB, etc. I'm sure I could even use ATAOE if needed