Prefered Filesystem for Shared disk for KVM

[Tomoki Taniguchi]

I am considering moving our ESXi server cluster to a KVM cluster.
Currently we are the FREE LICENSE version of ESXi for cost reasons.
This means no live migration and no centralized management.
Moving to KVM will give us these features.

Currently We have 4 ESXi servers connected to 2 iscsi disk servers
over a dedicated LAN.
The native VMFS handles the 2 iscsi servers nicely.

In trying to move the setup to a KVM cluster,
I am trying to figure out how to setup a shared storage-pool between
the KVM host machines to hold all the guest VMs.

I know it can be done with NFS, but when i was playing with XEN/NFS
I used to see a lot of performance issues. I am looking for an iscsi solution.

TIA,
TOmoki