When you use an ESXi system in conjunction with a SAN, you must decide whether array-based tools are more suitable for your particular situation.
When you consider an array-based solution, keep in mind the following points:
Array-based solutions usually result in more comprehensive statistics. With RDMs, data always takes the same path, which results in easier performance management.
Security is more transparent to the storage administrator when you use an RDM and an array-based solution because with RDMs, virtual machines more closely resemble physical machines.
If you use an array-based solution, physical compatibility RDMs are often used for the storage of virtual machines. If you do not intend to use RDMs, check the storage vendor documentation to see if operations on LUNs with VMFS volumes are supported. If you use array operations on VMFS LUNs, carefully read the section on resignaturing.