cbt_mode

--cbt_mode={on_if_enabled|on|off}

This parameter determines whether to use Changed Block Tracking (CBT) when performing an incremental or differential backup of an ESX(i) virtual machine.

Changed Block Tracking, a feature of ESX(i) 4.0 and later, tracks changes to the contents of virtual disks. This leads to faster backups and reduces the load on the storage during a backup.

Use of CBT is configured in the virtual machine settings. The CBT configuration parameters are set up independently for a virtual machine and for each of its disks. For information about setting up the CBT configuration parameters, refer to VMware Knowledge Base: http://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=1031873.

Acronis Backup enables you to start using CBT on multiple machines without having to manually set up multiple configuration parameters.

Available parameter values

• on (by default)

  Acronis Backup automatically enables CBT for each virtual machine that is backed up, and for all disks of the virtual machine. The resulting CBT settings determine CBT usage during the backup and are kept after the backup is completed.

• on_if_enabled

  If CBT is enabled for a virtual machine, Acronis Backup uses CBT according to the CBT settings of individual disks. Otherwise, CBT is not used.

  Use this value for all backups (including full ones) if you want to preserve your custom CBT settings for virtual machines.

• off

  Acronis Backup does not use CBT, regardless of the CBT settings for the virtual machines.

Restrictions

Because of the CBT support limitations in VMware vSphere, use of CBT is not possible in these cases:

• The virtual machine version is earlier than 7.
• The virtual machine has a Raw Device Mapping (RDM) disk attached in the physical compatibility mode.
• The virtual machine has a disk attached to a shared virtual SCSI bus. Use of CBT for the disk is possible only when the SCSI Bus Sharing setting is None.

The presence of snapshots, although it is a CBT support limitation in VMware vSphere, is not a restriction for using CBT in Acronis Backup.