vSAN -- Health Alarm -- "Thick-provisioned VMs on vSAN"

Products

• VMware vSAN

Issue/Introduction

vSAN Health is reporting the following Warning: "Thick-provisioned VMs on vSAN"

Example:

 

The Alarm details do show one or more Virtual Machine disks (= vmdk(s)) listed

Example:

 

 

Environment

vSAN All Versions

Cause

There are one or more Virtual Machine disk(s) on the vSAN Datastore which are thick-provisioned.

This may be caused by the Virtual Machine(s) being backed up from a SAN and restored to vSAN, regular storage vMotion shall always provision VMs with thin disks.

 

Resolution

The thick-provisioned config is applied via the vSAN Storage Policy assigned to the Virtual Machine Disk.

The setting in the vSAN Storage Policy where Thick provisioning of a Virtual Machine disk is called "Object Space Reservation"

It is possible that the Alarm shows up despite the applied vSAN Policy on the listed Virtual Machine disk(s) has Object Space Reservation set to 0 (= Thin-provisioned).

It is recommended to reclaim the underlying Storage allocation by changing the configuration from 'Thick' to 'Thin', which decrease vSAN Datastore utilization.

 

Change configuration from 'Thick' to 'Thin' by applying a cloned vSAN Storage Policy to the Virtual Machine disk(s) listed in the vSAN Alarm:

1.) Clone VM Storage Policy applied to the Virtual Machine disks listed in the vSAN Alarm

 

2.) Apply the cloned Policy to the listed Virtual Machine disk(s) listed in the vSAN Alarm

2.1) Right-click the VM in the vSphere Web Client navigator --> "Edit Settings"

2.2) Tab "VM Storage Policies" --> Edit the Storage policy --> Select the cloned Policy from the dropdown list and click "Apply to All". 

3.) Repeat Step 2.2) by applying the original applied vSAN Policy back (= the one which was cloned via Step 1.) )

Note:

• If there are any snapshots present on the VM, the disk provisioning would not change. Remove the snapshot and retry the solution.
• Sometimes, even after changing the provisioning back to thin, the skyline health alarm shows this VMs name. In those cases, restart the vmware-vsan-health service on the vCenter to fix the issue by using the below command:

service-control --restart vmware-vsan-health

Additional Information

• This Health Alarm will not check VMs deployed by ESX Agent Manager (EAM), as most of the VMs deployed are thick-provisioned by default or VMs with disabled tasks (vm.disabledMethod), for example, NSX Controllers

• With Virtual Machine disk(s) configured as "Thick provisioning", vSAN Datastore utilization will be higher. See KB 396137 and VMware Blog for additional information.