Virtual Machine Disk Consolidation Fails During Veeam Backup Operations

Products

• VMware vSphere ESX 7.x
• VMware vSphere ESX 8.x
• VMware vCenter Server

Issue/Introduction

Virtual machines display a "Virtual machine disk consolidation is needed" warning. In the vCenter Server "Recent Tasks" pane, the "Remove Snapshot" task may complete, but the subsequent "Consolidate virtual machine disk files" task fails.

• Remove Snapshot Reports consolidation failed
  
• Consolidate Virtual machine disk files task initiated via Veeam Reports- Unable to access file since it is locked An error occurred while consolidating disks: 

Failed to lock the file. Consolidation failed for disk node 'scsi0:1': Failed to lock the file. Consolidation failed for disk node 'scsio:O':

Failed to lock the file. Consolidation failed for disk node 'scsi0:0': Failed to lock the file.

• Datastore have orphaned delta disks (e.g., <VM_Name>-00000X.vmdk) remain present after the backup window has closed.
• Veeam appliance reports: VM has stuck snapshot, will attempt to consolidate periodically
  
• The Veeam backup appliance has high Max concurrent tasks setup
  

Environment

VMware vSphere 7.x

VMware vSphere 8.x

Cause

The failure is caused by a resource bottleneck on the backup proxy. If the backup appliance is configured to handle more concurrent tasks than the allocated vCPU resources on the proxy virtual machine (e.g., 32 tasks assigned to a proxy with only 16 vCPUs), the proxy cannot process the snapshot commit requests within the required timeframe. This leads to timeouts in the vSphere API calls responsible for disk consolidation.

Resolution

To resolve this issue, align the backup proxy resources with the workload volume:

1. Adjust Proxy Configuration:
• Access the backup software configuration console.
• Navigate to the Backup Proxy settings.
• Modify the Max Concurrent Tasks for the affected proxy.
• Ensure the number of concurrent tasks does not exceed the number of vCPUs allocated to that proxy virtual machine (1:1 ratio).
2. Manual Consolidation:
• In the vSphere Client, identify virtual machines with the "Consolidation Required" status.
• Right-click the virtual machine and select Snapshots > Consolidate.
• Confirm the task completes successfully and the delta files are consolidated.
3. Verify Proxy Resources:
• If high concurrency is required for the backup window, increase the vCPU allocation of the proxy virtual machine to match the desired task count, ensuring the underlying ESXi hosts have sufficient physical cores to back the allocation.