VM used space showing higher values than consumed space on UI and/or GuestOS disk usage

Products

• VMware vSAN
• VMware Cloud on AWS
• VMware Cloud on Dell EMC

Issue/Introduction

Impact/Risks:
This is a cosmetic issue, the used/consumed space discrepancy does not cause any impact to the environment or any of the vSAN functionalities.

 

Symptoms:
VM used space in vCenter UI may be bigger when comparing it to "Consumed Space" or "Disk used space" from GuestOS.

Environment

VMware vSAN (All Versions)

Cause

vCenter populates the UI with information about VM storage usage using different sources, this leads to a discrepancy when comparing the values from different perspectives (UI, VM view, Guest OS).

 

By design, vSAN OSA allocation of new blocks is performed at 4MB chunks except when vSAN OSA space efficiency technologies (Compression Only, Deduplication) are in use, which in turn uses 4KB chunks. In this scenario, if the VM data allocation is sparse, it may report more space consumption.

Resolution

This cosmetic issue has been fixed in 8.0U3. Both vCenter and ESXi are required to be upgraded to 8.0U3.

 

For those using the VMC platform please file a Support Request, if the 'actual value' is needed as VMware Support will need to run the command to gather these details.

Workaround:

Starting from vSAN 8.0, a new data field was added to the output of the "esxcli vsan debug object list" command.
This new field is "Used 4K Blocks:" and it's the most accurate value when trying to identify how much a vSAN object is consuming, for example:

Object UUID: 7536ae61-####-####-####-########a9c
   Version: 15
   Health: healthy
   Owner: ###-10-###-244-1.eng.com
   Size: 1024.00 GB
   Used: 5.59 GB <----------------------------- old counter
   Used 4K Blocks: 1.35 GB <------------------- new counter, already showing a huge difference

 

The Cluster level vSAN usage information, found by following this path in vCenter "Cluster -> Monitor -> vSAN -> Capacity", has been confirmed to be showing the correct value. 

Additional Information