When using ESXi with a SAN, you must follow specific guidelines to avoid SAN problems.
Observe the following 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 configuration, access control, storage, switch, server and iSCSI 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.
Cross off different links, switches, HBAs, and other elements to ensure that you did not miss a critical failure point in your design.
Ensure that the iSCSI HBAs are installed in the correct slots in the ESXi 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 ESXi performance charts, Ethernet switch statistics, and storage performance statistics.
Change LUN IDs only when VMFS datastores deployed on the LUNs have no running virtual machines. If you change the ID, virtual machines running on the VMFS datastore might fail.
After you change the ID of the LUN, you must rescan your storage to reset the ID on your host. For information on using the rescan, see Storage Rescan Operations.
If you change the default iSCSI name of your iSCSI adapter, make sure that the name you enter is worldwide unique and properly formatted. To avoid storage access problems, never assign the same iSCSI name to different adapters, even on different hosts.