When authorizing access to a volume, the Challenge-Handshake Authentication Protocol (CHAP) can be invoked in conjunction with the iSCSI initiator ID for added security. For our volume Win02, which contained a VM running Windows Server 2003, we granted full access to both of our ESX servers via their VMware iSCSI initiator. The VMFS DLM ensured that only one server at a time could open and start the Win02 VM image.