"By default, the SCSI controller is assigned to virtual device node (z:7), so that device node is unavailable for hard disks or SCSI devices."
Source: https://pubs.vmware.com/vsphere-51/index.jsp?topic=%2Fcom.vmware.vsphere.vm_admin.doc%2FGUID-5872D17...
SCSI Controller Configuration
To access virtual disks and SCSI devices, a virtual machine uses virtual SCSI controllers. These virtual controllers appear to a virtual machine as different types of controllers, including BusLogic Parallel, LSI Logic Parallel, LSI Logic SAS, and VMware Paravirtual SCSI. You can add a SCSI controller, change the SCSI controller type, and select bus sharing for a virtual machine.
Each virtual machine can have a maximum of four SCSI controllers. The default SCSI controller is numbered as 0. When you create a virtual machine, the default hard disk is assigned to the default SCSI controller 0 at bus node (0:0).
When you add SCSI controllers, they are numbered sequentially 1, 2, and 3. If you add a hard disk or SCSI device to a virtual machine after virtual machine creation, it is assigned to the first available virtual device node on the default SCSI Controller, for example (0:1).
If you add a SCSI controller, you can reassign an existing or new hard disk, or a SCSI device, to that controller. For example, you can assign the device to (1:z ), where 1 is SCSI Controller 1 and z is a virtual device node from 0 to 15.
By default, the SCSI controller is assigned to virtual device node (z:7), so that device node is unavailable for hard disks or SCSI devices.
