Understanding the Difference Between VMware Datastore Usage and Dell PowerStore LUN Provisioned Capacity

Products

• VMware vSphere ESXi

Issue/Introduction

Customers may observe that the datastore capacity displayed on the ESXi host is lower than the provisioned space reported on the corresponding Dell PowerStore storage array.

Below screenshot gives an idea how the re-presentation looks like when the issue is observed::

Space Allocation from Storage side: 

Space Allocation from vCenter/ESXi Host side: 

Environment

VMware vCenter 8.x

VMware vSphere ESXi 8.x

Cause

• This discrepancy is typically expected behavior due to Unmapped LUNs/Volumes: Only volumes that are actively mapped to ESXi hosts are presented to vCenter.

• If volumes are provisioned on the array but have 'Host Mapping = 0', they will not contribute to the datastore capacity in VMware

Resolution

To validate the storage computation and resolve the perceived mismatch, perform the following steps:

1: Verify Host Mapping on Storage Array

1. Log in to the backend storage management interface (e.g., PowerStore Manager).
2. Navigate to the Volumes or Storage section.
3. Identify all provisioned volumes and check the Host Mapping column
4. Confirm if the 'missing' capacity corresponds to volumes with zero mappings. These volumes must be mapped to the ESXi cluster to be visible in vCen

2: Calculate Mapped Capacity

Compare the sum of all "mapped volumes" on the array to the total capacity shown in vCenter.

Example Calculation: 

• Array Total Provisioned: 80 TB

• Mapped Volumes (e.g., 5 x 12 TB PROD volumes): 60 TB

• Unmapped Volumes (e.g., 2 x 10 TB DR volumes): 20 TB

Result: vCenter correctly displays 60 TB of storage, which corresponds to the volumes mapped from the storage array, while the remaining unmapped 20 TB is intentionally unavailable to the hosts.