You must meet several requirements for your ESXi host to work properly with a SAN.
Verify that your SAN storage hardware and firmware combinations are supported in conjunction with ESXi systems. For an up-to-date list, see vSphere Compatibility Guide.
Configure your system to have only one VMFS datastore for each LUN.
Unless you are using diskless servers, set up a diagnostic partition on a local storage. If you have diskless servers that boot from iSCSI SAN, see General Boot from iSCSI SAN Recommendations for information about diagnostic partitions with iSCSI.
Use RDMs for access to any raw disk. For information, see Raw Device Mapping.
Set the SCSI controller driver in the guest operating system to a large enough queue. For information on changing queue depth for iSCSI adapters and virtual machines, see vSphere Troubleshooting.
On virtual machines running Microsoft Windows, increase the value of the SCSI TimeoutValue parameter to allow Windows to better tolerate delayed I/O resulting from path failover. For information, see Set Timeout on Windows Guest OS.