Datastore usage is higher than shown on array

Products

• VMware vSphere ESXi

Issue/Introduction

The Storage amount in vCenter shows different amount than on the physical Storage Array (e.g. Dell PowerStore).

The display in vCenter, on the Host UI, and the df output matches, but the Storage Array display shows a lower amount of used space.

 

Resolution

This is expected as most modern storage arrays have space saving technologies. These savings are invisible to the 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

 

If you are concerned that these numbers are inaccurate, compare the total file usage by:

A.) 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 )