VM's provisioned Storage, used Storage show larger than allocated disk space.

Products

• VMware vSphere ESXi

Issue/Introduction

• Virtual Machines used storage, provisioned storage show much bigger values than actual allocated Storage space on the vSphere client. 

There may be no visible impact on VM's operations tasks.

 

Environment

VMware vSphere ESXi

VMware vCenter Server 

Third Party Backup tool / Software 

Thin Provisioned VM disks

Cause

• The discrepancy between the VM's reported provisioned or used storage and its original allocated disk space is typically attributed to the presence and growth of one or more virtual machine snapshots.

 

Resolution

The recommended solution is to perform a snapshot consolidation by deleting the existing snapshots using the VM's Snapshot Manager .Step-by-Step Resolution

1. Evaluate Current VM State and Impact:
   
   
   • Assess the VM's current operational status and performance. Large, unmanaged snapshots can cause I/O performance degradation on the VM and strain the underlying ESXi host.
   • Identify the exact number and age of the snapshots in the Snapshot Manager. Snapshots should be a temporary solution, not a permanent part of the VM's configuration.
     
     
2. Power Off the VM (Recommended for Safety and Speed):
   
   
   • Action: If possible, gracefully shut down (power off) the Virtual Machine before proceeding with the deletion/consolidation.
     
     
   • Rationale:
     • Expedited Consolidation: Snapshot consolidation (the process of merging delta files back into the base disk) is significantly faster when the VM is powered off, as the system does not have to manage live disk I/O during the process.
     • Risk Mitigation: It is the safest method, eliminating the risk of data corruption or instability that can sometimes occur during consolidation on a highly active, running VM, especially if the snapshots are very large.
       
       
3. Delete/Consolidate Snapshots via Snapshot Manager: 
   
   
   • Action: Access the VM's Snapshot Manager. Select the option to "Delete All" or "Consolidate" snapshots.
     
     
   • Rationale:
     • "Delete All" removes all existing snapshot states and merges the data from all delta files into the original base disk. This is the preferred method to fully resolve the storage issue.
     • The process of consolidation merges the chain of delta files, one by one, until all changes are committed to the base disk. The delta files are then removed, freeing up the excess provisioned storage space.
       
       
4. Verify Disk Space and Operation:
   
   
   • Action: After the consolidation process completes, verify that the storage utilization has returned to the expected size (the original allocated disk space).
   • Action: Power the VM back on and monitor its performance to ensure stability and that the initial storage reporting issue is resolved.

** Critical Note on Snapshot Consolidation

• Required Free Space: Ensure that the datastore/storage system hosting the VM has sufficient free space to accommodate the consolidation process. While the consolidation reduces the overall footprint, it temporarily requires space to perform the merge operation before the old delta files are deleted. A general rule is to have at least the size of the largest delta disk file available.
  
  
• Backup Policy Review: After resolving the issue, review the backup tool's configuration to ensure it is properly configured to clean up (delete/consolidate) snapshots immediately after a successful backup job. This prevents the recurrence of the problem.