This topic provides general information about how to allocate LUNs when your ESX/ESXi works in conjunction with SAN.

When you set LUN allocations, be aware of the following points:

Storage provisioning

To ensure that the ESX/ESXi system recognizes the LUNs at startup time, provision all LUNs to the appropriate HBAs before you connect the SAN to the ESX/ESXi system.

VMware recommends that you provision all LUNs to all ESX/ESXi HBAs at the same time. HBA failover works only if all HBAs see the same LUNs.

For LUNs that will be shared among multiple hosts, make sure that LUN IDs are consistent across all hosts. For example, LUN 5 should be mapped to host 1, host 2, and host 3 as LUN 5.

vMotion and VMware DRS

When you use vCenter Server and vMotion or DRS, make sure that the LUNs for the virtual machines are provisioned to all ESX/ESXi hosts. This provides the most ability to move virtual machines.

Active/active compared to active-passive arrays

When you use vMotion or DRS with an active-passive SAN storage device, make sure that all ESX/ESXi systems have consistent paths to all storage processors. Not doing so can cause path thrashing when a vMotion migration occurs.

For active-passive storage arrays not listed in the Storage/SAN Compatibility Guide, VMware does not support storage port failover. In those cases, you must connect the server to the active port on the storage array. This configuration ensures that the LUNs are presented to the ESX/ESXi host.