Knowledge Base

Table 1. Controller Support Matrix

[1] Both AHCI/SATA and IDE/ATA mode is supported. However, in IDE/ATA mode, ESXi Installable is not supported.

[2] A maximum of 10 virtual machines are supported on these VMFS.

For controllers that support both AHCI/SATA and IDE/ATA you should be aware of the following trade-offs.

• If you are using AHCI/SATA mode on SATA optical drive, the guest operating system does not have access to the optical drive. Only VMkernel and service console have access to the optical drive. This limitation is removed in ESX Server 3.5 Update 5.
• If you are using IDE/ATA mode, VMFS is not supported.
• ESX Server 3.5 Update 4 and earlier, export only IDE CD-ROM devices to the guest operating system. They do not export SCSI CD-ROM to the guest operating system. In other words, the guest operating system can attach CD-ROM devices only by using an IDE controller. You cannot attach CD-ROM devices using SCSI controller because ESX does not support connecting SCSI CD-ROMs or ISO images, even if the underlying ESX storage driver exposes SCSI interface to VMkernel. This limitation is removed starting from ESX Server 3.5 Update 5 with the support for SCSI CD-ROM drive in the AHCI/SATA mode.
• While running in AHCI/SATA mode, ESX loads its AHCI drivers which enable I/O access to a CD-ROM or hard-drive connected through an I/O Controller Hub (ICH). AHCI is a SCSI-based driver that exports SCSI interface to VMkernel. However, in earlier releases of ESX Server 3.5 Update 5, the guest operating system does not have direct CD-ROM access because this is a SCSI-based CD-ROM.
• While running in IDE/ATA mode, ESX loads its IDE-based drivers which enable I/O access to a CD-ROM or hard-drive connected through an I/O Controller Hub (ICH). Guest operating systems have CD-ROM access because this is an IDE-based CD-ROM. However, I/O speed to the hard drive is slower than in AHCI/SATA mode, which is why most high-end servers do not use IDE/ATA mode for hard drive use.
• For hard drive usage, note that by design, VMFS datastores cannot be created on an IDE-based interface. For an AHCI/SATA based interface, while it is technically possible to create a VMFS datastore on these SCSI-based drives, such a configuration is not supported by VMware mainly because SATA protocol does not support reserve/release. Reserve/release is needed if VMFS is used as a clustered file system in a shared disk environment. The following table-2 and diagram-1 summarizes the behavior
  

Table 2. Feature Support Matrix

[1] Available only in ESX Server 3.5 Update 5, ESX 4.0 and later.

[2] This is a known limitation.

 

• This image is not applicable for ESX Server 3.5 Update 5, ESX Server 4.0 or later. Starting from ESX Server 3.5 Update 5 supports SCSI CD-ROM access from the guest operating system.
• ESX Server automatically determines which mode to run (either IDE/ATA or AHCI/SATA) based on the BIOS setting in the machine.

• Does the guest operating system/CD-ROM access limitation only apply to ESX 3i (embedded)? What about classic ESX?
  
  This limitation applies to both ESX 3i (embedded) and ESX 3.5. However, this limitation is removed starting from ESX Server 3.5 Update 5.
  
• In ESX Server 3.5 Update 4 and earlier, the system allows the guest operating system to directly access the CD-ROM. Why is it mentioned that in ESX 3.5 Update 4 the guest operating system might not have CD-ROM access? What has changed?
  
  In earlier releases, the system allows the guest operating system to access CD-ROM because ESX 3.5 uses IDE/ATA interface and not AHCI/SATA interface. In ESX 3.5 Update 4, if you continue to use IDE/ATA interface, the guest operating system also continues to have CD-ROM access. This feature has changed. With the introduction of AHCI/SATA support in ESX 3.5 Update 3, currently, the server vendor can configure the I/O controller either in IDE/ATA or AHCI/SATA.
  For example, if you are using ESX Server 3.5 Update 4 or an earlier release and the server is configured with the ICH10 controller to use AHCI/SATA mode, then the guest operating system does not have CD-ROM access. However, in ESX Server 3.5 Update 5, the guest operating system has access to CD-ROM if the server is using either IDE/ATA interface or AHCI/SATA interface.
  

• In ESX Server 3.5 Update 5, how do I add a SCSI CD-ROM or DVD drive to a virtual machine?
  
  To add a SCSI CD-ROM or DVD drive.

  1. Edit the virtual machine settings and move the SCSI drive to scsi0:1 instead of scsi0:0.

  2. Save this settings.

  3. Edit the virtual machine settings and add the new SCSI CDROM type device to the virtual machine as scsi0:0.

  4. Save the setting.

Note: For a complete list of supported guest operating systems, see the VMware Compatibility Guide.