Reducing VM storage consumption on VSAN datastore

Products

• VMware vSAN

Issue/Introduction

VM storage utilization on vSAN datastore shows higher than the actual usage.

Environment

VMware vSAN 8.x
VMware vSAN 7.x
VMware vSAN 6.x

Cause

VM configured on the storage policy "Stretched - Site Mirror" with "Raid-1, hostFailuresToTolerate: 1" policy with "Thick provision" Disks.

Policy:
  stripeWidth: 1
      cacheReservation: 0
      proportionalCapacity: 100    >>>>>>>>> (proportionalCapacity: 100 refers to Thick provision , proportionalCapacity: 0 regfers to Thin provision)
      hostFailuresToTolerate: 1    
      forceProvisioning: 0
      spbmProfileId: xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx
      spbmProfileGenerationNumber: 0
      replicaPreference: Performance   >>>>>>> ( Performance refers to Raid 1)
      iopsLimit: 0
      checksumDisabled: 0
      subFailuresToTolerate: 1
      CSN: xxxx
      SCSN: xxxx
      spbmProfileName: Stretched - Site Mirror
      locality: None

• "Stretched - Site Mirror" with "Raid-1, hostFailuresToTolerate: 1": This policy results in a 4x capacity consumption compared to the actual data usage, as it mirrors the data on other site.
• Thick provisioning is a type of storage pre-allocation. With thick provisioning, the complete amount of virtual disk storage capacity is pre-allocated on the physical storage when the virtual disk is created. A thick-provisioned virtual disk consumes all the space allocated to it in the datastore right from the start, so the space is unavailable for use by other virtual machines.

Resolution

Transitioning to thin provisioning reclaims unwritten storage space while retaining RAID-1 data protection.

1. Log in to the vSphere Client.
2. Navigate to Policies and Profiles > VM Storage Policies.
3. Click Create VM Storage Policy.
4. Provide a name, such as "vSAN-Thin-RAID1".
5. Enable rules for vSAN storage.
6. Set Failures to Tolerate to 1 failure - RAID-1 (Mirroring).
7. Set Object Space Reservation to Thin provisioning (0%).
8. Complete the wizard and verify datastore compatibility.
9. Right-click the target VM and select VM Policies > Edit VM Storage Policies.
10. Apply the new policy and monitor reconfiguration in the Resyncing Objects view.

OR

Apply a suitable storage policy to the VM which results in lesser capacity consumption compared to the old policy Stretched - Site Mirror with Raid-1, hostFailuresToTolerate: 1.

Additional Information

• Changing the storage policy may trigger a resync, which could impact performance. Therefore, it’s recommended to update the VM policy during off-business hours.
• Ensure VM disks are not running on Snapshots
• Verify that all disks are compliant with the current storage policy.