When you use ESXi with a Fibre Channel SAN, follow specific guidelines to avoid SAN problems.
To prevent problems with your SAN configuration, observe these tips:
Place only one VMFS datastore on each LUN.
Do not change the path policy the system sets for you unless you understand the implications of making such a change.
Document everything. Include information about zoning, access control, storage, switch, server and FC HBA configuration, software and firmware versions, and storage cable plan.
Plan for failure:
Make several copies of your topology maps. For each element, consider what happens to your SAN if the element fails.
Verify different links, switches, HBAs, and other elements to ensure that you did not miss a critical failure point in your design.
Ensure that the Fibre Channel HBAs are installed in the correct slots in the host, based on slot and bus speed. Balance PCI bus load among the available buses in the server.
Become familiar with the various monitor points in your storage network, at all visibility points, including host's performance charts, FC switch statistics, and storage performance statistics.
Be cautious when changing IDs of the LUNs that have VMFS datastores being used by your ESXi host. If you change the ID, the datastore becomes inactive and its virtual machines fail. Resignature the datastore to make it active again. See Managing Duplicate VMFS Datastores.
After you change the ID of the LUN, rescan the storage to reset the ID on your host. For information on using the rescan, see Storage Rescan Operations.