Adding a Hard Disk to a Virtual Machine in the vSphere Client
When you add a hard disk to a virtual machine (VM), you can create a new virtual disk, add an existing virtual disk, or add a mapped Storage Area Network (SAN) Logical Unit Number (LUN).
In most cases, you can accept the default device node. For a hard disk, a nondefault device node is useful to control the boot order or to have different Small Computer System Interface (SCSI) controller types. For example, you might want to boot from an LSI Logic controller and use a Buslogic controller with bus sharing turned on to share a data disk with another VM.