Persistent binding is highly recommended in a SAN environment especially when several storage subsystems are available to the VMware ESX Server.
The storage SCSI ID, in a SAN, is dictated by the order in which the VMware ESX Server will discover the subsystems at boot time. In some instances, this order might differ because of a device addition or removal. This could cause VMware ESX Server to assign a different Target ID and change the device addressing (vmhba <C> : <T> : <D>). This can cause the virtual machines to report their storage as missing when booting. Using the persistent binding will force VMware ESX Server to always use the same Target ID for a storage unit no matter of the discovery order.
To enable persistent binding on all adapters use the command: pbind.pl -A