vCenter client shows incorrect size for VM snapshot

Products

• VMware vSphere ESXi

Issue/Introduction

Wanting to confirm the actual size of the VM snapshot before deleting (consolidating) it.

• RDM disks attached to VM in "Physical" mode.
• At least one standard VMFS disk attached to VM.
• Size for VM snapshot listed as full RDM size (e.g., multiple RDM disks - 1TB, 2TB, 15TB = 18TB - vCenter lists snapshot size of 18TB).
• ESX running newer build than vCenter server.

Environment

vCenter server 8.0 U3 (Base)

vSphere ESX 8.0 U3e

Cause

It is possibly due to how vCenter sees the "physical" RDM disks, instead of only based on the actual snapshot files ("sesparse" or "delta").

• It may also be due to the running ESX build being newer than the running VCSA build.

Resolution

Confirm the existence of snapshot files ("sesparse" or "delta") and their actual sizes.

• Via SSH connect to an ESX host that has access to the shared storage the VM resides on, and log in as root user.
• Navigate to the VM folder.
  
  cd /vmfs/volumes/<datastore_name>/<vm_name>/
  
  
  
• View the VM files looking for any snapshot files for each disk.
  
  ls -lah
  
  
• Confirm the snapshot files listed match those being used in the VM config via the vSphere client VM disks view. (e.g., "<vm_name>...2-0001.vmdk", etc.).

 

Calculate the actual snapshot size by combining all listed snapshot files for each disk. If the RDM disks are "Physical" mode, there should be no snapshot files listed for those disks.

• You can also run the below command from KB "How to calculate current snapshot size, estimate consolidation time and understand performance factors affecting the consolidation process." to calculate the actual size.
  
  ls -la | grep 'delta|sesparse' | awk '{print $5}' | awk '{ SUM += $1/1024/1024 } END {print "Total Snapshot Size: " SUM " MB"}'

 

It is possible a fix for the vCenter displaying incorrect snapshot size value is in a later build.

• Note: It is recommended to keep the vCenter server build at least the same or newer than the ESX hosts it manages, and keeping the vSphere updated to the latest builds available.