To access virtual disks, CD/DVD-ROM, and SCSI devices, a virtual machine uses storage controllers, which are added by default when you create the virtual machine. You can add additional controllers or change the controller type after virtual machine creation. You can make these changes while you are in the creation wizard. If you know about node behavior, controller limitations, and compatibility of different types of controllers before you change or add a controller, you can avoid potential boot problems.

How Storage Controller Technology Works

Storage controllers appear to a virtual machine as different types of SCSI controllers, including BusLogic Parallel, LSI Logic Parallel, LSI Logic SAS, and VMware Paravirtual SCSI. AHCI, SATA, and NVMe controllers are also available.

When you create a virtual machine, the default controller is optimized for best performance. The controller type depends on the guest operating system, the device type, and sometimes, the virtual machine's compatibility. For example, when you create virtual machines with Apple Mac OS X guests and ESXi 5.5 and later compatibility, the default controller type for both the hard disk and the CD/DVD drive is SATA. When you create virtual machines with Windows Vista and later guests, a SCSI controller is the default for the hard disk and a SATA controller is the default for the CD/DVD drive.

Each virtual machine can have a maximum of four SCSI controllers and four SATA controllers. The default SCSI or SATA controller is 0. When you create a virtual machine, the default hard disk is assigned to the default controller 0 at bus node (0:0).

When you add storage controllers, they are numbered sequentially 1, 2, and 3. If you add a hard disk, SCSI, or CD/DVD-ROM device to a virtual machine after virtual machine creation, the device is assigned to the first available virtual device node on the default controller, for example (0:1).

If you add a SCSI controller, you can reassign an existing or new hard disk or 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. For SCSI controllers, z cannot be 7. By default, the virtual SCSI controller is assigned to virtual device node (z:7), so that device node is unavailable for hard disks or other devices.

If you add a SATA controller, you can reassign an existing or new hard disk or device to that controller. For example, you can assign the device to (1:z ), where 1 is SATA controller 1 and z is a virtual device node from 0 to 29. For SATA controllers, you can use device nodes 0 through 29, including 0:7.

Alternatively, each virtual machine can have a maximum of four NVMe controllers. You can reassign an existing or new hard disk or device to that controller. For example, you can assign the hard disk to (x:z ), where x is NVMe controller and z is a virtual device node. x has values from 0 to 3, and z has values from 0 to 14.

Storage Controller Limitations

Storage controllers have the following requirements and limitations:

  • LSI Logic SAS and VMware Paravirtual SCSI are available for virtual machines with ESXi 4.x and later compatibility.
  • AHCI SATA is available only for virtual machines with ESXi 5.5 and later compatibility.
  • NVMe is available only for virtual machines with ESXi 6.5 and later compatibility.
  • BusLogic Parallel controllers do not support virtual machines with disks larger than 2TB.
Caution: Changing the controller type after the guest operating system is installed will make the disk and any other devices connected to the adapter inaccessible. Before you change the controller type or add a new controller, make sure that the guest operating system installation media contains the necessary drivers. On Windows guest operating systems, the driver must be installed and configured as the boot driver.

Storage Controller Compatibility

Adding different types of storage controllers to virtual machines that use BIOS firmware can cause operating system boot problems. In the following cases, the virtual machine might fail to boot correctly and you might have to enter the BIOS setup and select the correct boot device:
  • If the virtual machine boots from LSI Logic SAS or VMware Paravirtual SCSI, and you add a disk that uses BusLogic, LSI Logic, or AHCI SATA controllers.
  • If the virtual machine boots from AHCI SATA, and you add BusLogic Parallel or LSI Logic controllers.

Adding additional disks to virtual machines that use EFI firmware does not cause boot problems.

Table 1. VMware Storage Controller Compatibility
Existing Controller Added Controller
BusLogic Parallel LSI Logic LSI Logic SAS VMware Paravirtual SCSI AHCI SATA IDE NVME
BusLogic Parallel Yes Yes Yes Yes Yes Yes Yes
LSI Logic Yes Yes Yes Yes Yes Yes Yes
LSI Logic SAS Requires BIOS setup Requires BIOS setup Usually Works Usually Works Requires BIOS setup Yes Usually Works
VMware Paravirtual SCSI Requires BIOS setup Requires BIOS setup Usually Works Usually Works Requires BIOS setup Yes Usually Works
AHCI SATA Requires BIOS setup Requires BIOS setup Yes Yes Yes Yes Yes
IDE Yes Yes Yes Yes Yes N/A Yes
NVME Requires BIOS setup Requires BIOS setup Usually Works Usually Works Requires BIOS setup Yes Usually Works