Workflow of incremental backup based on changed block tracking
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Workflow of incremental backup based on changed block tracking


Article ID: 344418


Updated On:


VMware vSphere ESXi


This article provides steps for CBT incremental backup.


Virtual Disk Development Kit 6.5
Virtual Disk Development Kit 5.5
Virtual Disk Development Kit 6.7
Virtual Disk Development Kit 6.0
Virtual Disk Development Kit 5.1
Virtual Disk Development Kit 5.0


  1. Enable CBT using the Knowledge Base article Enabling or disabling Changed Block Tracking (CBT) on virtual machines.
  2. Take a snapshot (SN-1) and call QueryChangedDiskAreas(*) or VixDiskLib_QueryAllocatedBlocks for full backup.
  3. Record the changeId (CID-1) of SN-1.
  4. Remove SN-1.
  5. Run the VM for some time (backup interval).
  6. Take a snapshot (SN-2) and call QueryChangedDiskAreas with previous changeId (CID-1) to get changes after taking that snapshot (SN-1).
  7. Record the changeId (CID-2) of SN-2.
  8. Remove SN-2.
  9. Repeat step 5-8 (replace changeId accordingly).
Note: VixDiskLib_QueryAllocatedBlocks always returns all allocated disk areas regardless of CBT. It is a VDDK API which is applicable for on-prime environment but not VMC.