This value is the unique identifier of a VSAN (Virtual Storage Area Network) on the device and serves as the index for rows in the VSAN configuration and domain-management tables. Admins use it to distinguish between multiple isolated Fibre Channel fabrics configured on the same switch, since VSANs let one physical device support several logically separate SANs. For example, hh3cVsanIndex value 10 would identify a specific VSAN whose core switch name, domain ID, and fabric state are all looked up via that same index in the related hh3cVsanDmTable.