CBT technology can be used to improve efficiency when backing up VMs on SCP and HCI through third-party backup apps. If CBT is not enabled, only full backups are supported, meaning all data of snapshots needs to be backed up. When CBT is enabled, bitmaps can be used to back up only incremental data in data blocks.

For VMs with CBT enabled, a bitmap checkpoint (referred to as a Check Point) is created when a snapshot is taken. The checkpoint ID (CheckPointID) represents the bitmap of data blocks that have changed between the current snapshot and the previous one. SCP and HCI provide OpenAPIs for querying CBT bitmaps and querying changed data blocks between a specified checkpoint and the latest snapshot.

Notes:

1. For the initial backup, set the checkpoint value to 0 (CheckPointID=0) to query the CBT bitmap of all changed data blocks at the current snapshot point.
2. For sequent backups, specify the CheckPointID of the last backup to query the CBT bitmap of data blocks that have changed between that checkpoint and the current snapshot point.
3. For capacity-intensive disks, the OpenAPI for querying the CBT bitmap may not return the full bitmap at a single request. In such cases, multiple API calls may be required to obtain all changed data blocks.
4. If the API returns the error message "The VM CBT has expired. Please reset it.", operations such as snapshot recovery and backup recovery may have been performed on the VM. In this case, please reset the CBT bitmap first.
5. CBT can be enabled selectively for specific disks of a VM because enabling CBT may impact disk write performance.