Problem
VMware virtual machine backup jobs in Druva Phoenix fail during the snapshot creation and Changed Block Tracking (CBT) validation phase.
The backup operation aborts with one or both of the following errors:
One or more VM snapshot exists, can not reset the CBTAnother task is already in progress
Cause
This issue is caused by two distinct VMware-side conditions preventing Druva from successfully processing the backup:
1. CBT Reset Conflict
Druva detected inconsistencies with Changed Block Tracking (CBT) and attempted to reset it automatically to ensure backup integrity. However, VMware API constraints strictly prohibit resetting CBT while any snapshots exist on the virtual machine. These can include:
Manual snapshots
Orphaned or stale snapshots from previous operations
Failed backup snapshots that were not automatically consolidated
2. VMware Task Lock (Reconfigure Task)
While Druva was attempting to request a backup snapshot, VMware vCenter/ESXi reported that another major configuration-related task was already executing on the target VM. VMware permits only one major reconfigure task at a time per object. A stuck or actively running Reconfigure Virtual Machine task will block Druva's snapshot request.
Traceback
Review the Druva Phoenix backup logs or agent logs. You will see errors matching the following patterns:
CBT Reset Failure
message="One or more VM snapshot exists, can not reset the CBT." filename=cbtmanager.go:413 message="Failed to reset CBT" Error="One or more VM snapshot exists, can not reset the CBT."
Snapshot Creation & Task Lock Failures
message="VM snapshot creation failed." Error="Another task is already in progress." Error="code: 4296146951, msg: Another task is already in progress." actualErrType: *types.TaskInProgress message="Failed to create backup snapshot" Error="Another task is already in progress." message="Aborting backup operation" error="Another task is already in progress."
Resolution
Follow these steps sequentially to clear the VMware blocks and resume backups:
Step 1: Clear Existing VMware Snapshots
Log in to the VMware vSphere Client.
Navigate to the affected virtual machine.
Right-click the VM and open the Snapshot Manager (Snapshots -> Manage Snapshots).
Verify if any snapshots are present.
If snapshots exist, select Delete All or perform a Consolidate operation.
Wait for the vSphere snapshot consolidation task to complete 100% successfully.
⚠️ Note: The CBT reset operation will continue to fail until all snapshots are completely removed from the VM's disk chain.
Step 2: Resolve VMware "Task in Progress" Condition
In vCenter, select the affected VM and look at the Recent Tasks pane at the bottom.
Check for active or hung tasks such as Reconfigure Virtual Machine, Create Snapshot, or Consolidate virtual machine disk.
If the task is actively running: Allow the vSphere task to complete naturally before restarting the Druva backup.
If the task is hung or "ghosted": You must clear the lock. This typically requires restarting the VMware management agents on the specific ESXi host hosting the VM:
SSH into the ESXi host as root and run:
/etc/init.d/hostd restart /etc/init.d/vpxa restart
Verify in vCenter that the stuck task has cleared.
Step 3: Retry the Backup Job
Once the snapshots are consolidated and the VMware task locks are cleared, log into the Druva Phoenix Console, select the VM, and trigger an on-demand backup job. Druva will now be able to reset the CBT and create its temporary backup snapshot successfully.