VMFS Datastore Usage is higher than shown on Physical Storage Array

Products

• VMware vSphere ESXi
• VMware vSphere ESXi 8.0

Issue/Introduction

VMFS Datastore shows a higher usage than on the actual Storage Array (via related App).

For example when using: Dell PowerStore, Dell/EMC Unisphere for PowerMax

 

Despite the following circumstances:

• Completed Rescan Operations
• Enabled automatic Space Reclamation on the VMFS Datastore
• vSphere and Storage Array do show the same Datastore Capacity (in example below it shows 20 TB) 

 

The issue exits no matter where the VMFS Datastore usage is determined, for example via:

• vSphere Client
• Command line on the ESXi Host
• ESXi Host Client 

 

 

Example:

 

 

 

 

 

Environment

vSphere ESXi

Cause

This is expected as most modern Storage arrays have space saving technologies.

These savings are invisible to the ESXi Hosts and vCenter, and are therefore not accounted for at that layer. 

Some examples of these Technologies:

• Thick provision - lazy zero
• Zero block discard
• Deduplication
• Compression

Resolution

Contact your HW Storage Vendor for further information on used Space saving Technologies on your Storage Array.

 

Additional Information

• Reference from Dell/EMC: Dell Unity: Difference between VMware Level Datastore Usage and Unity Storage LUN Usage

• If there are concerns that these numbers are inaccurate, compare the total file usage by:

Open a SSH/Putty Session to one of the Hosts connected to the affected Datastore

Compare the output of the command "du" to the output of the command "df"

along with the information shown in the Host UI ( Host Client ) and vCenter vSphere Client ( Web Client )