ESXi supports a variety of SAN storage systems in different configurations. Generally, VMware tests ESXi with supported storage systems for basic connectivity, HBA failover, and so on.

Not all storage devices are certified for all features and capabilities of ESXi, and vendors might have specific positions of support with regard to ESXi.

Basic connectivity
Tests whether ESXi can recognize and operate with the storage array. This configuration does not allow for multipathing or any type of failover.
HBA failover
The server is equipped with multiple HBAs connecting to one or more SAN switches. The server is robust to HBA and switch failure only.
Storage port failover
The server is attached to multiple storage ports and is robust to storage port failures and switch failures.
Boot from SAN
The host boots from a LUN configured on the SAN rather than from the server itself.
Direct connect
The server connects to the array without using switches. For all other tests, a fabric connection is used. FC Arbitrated Loop (AL) is not supported.
Clustering
The system is tested with Microsoft Cluster Service running in the virtual machine.