vSAN Health alert "Thick-provisioned VMs on vSAN" triggered against virtual machine(s) with a thin provisioned vSAN storage policy

Products

• VMware vSAN

Issue/Introduction

• In vSphere Client: 
  • vSAN Cluster -> [Monitor] > [vSAN] -> [Skyline Health] -> Health check "Thick-provisioned VMs on vSAN" shows one or more virtual machine(s) and their respective disk(s) as thick provisioned. 
  • Affected virtual machine(s) > [Summary] -> [VM Hardware] shows virtual disk(s) as thick provisioned. 
    
    
• On the other hand, all virtual machine specific configurations indicate thin provisioned. 
  • A thin provisioned (object space reservation = 0%) vSAN storage policy is applied to the virtual machine(s) and the compliance status is "Compliant". 
  • ddb.thinProvisioned = "1" is set in respective vmdk descriptor file(s). 

Environment

VMware vSAN

Cause

The virtual disk(s) are unexpectedly flagged as thick provisioned (thinProvisioned = false) on an ESXi host. It is detected as "Thick-provisioned VMs on vSAN" alert. 

vim-cmd vmsvc/device.getdevices
....
         backing = (vim.vm.device.VirtualDisk.FlatVer2BackingInfo) {
            fileName = "[vsanDatastore] XXXXXXXX-XXXX-XXXX-XXXX-XXXXXXXX/example.vmdk",
            datastore = 'vim.Datastore:vsan:XXXXXXXXXXXXXXXX-XXXXXXXXXXXXXXXX',
            backingObjectId = "XXXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXX",
            diskMode = "persistent",
            split = false,
            writeThrough = false,
            thinProvisioned = false, <======== !!!!!
....

Resolution

Performing vMotion the affected virtual machines to a different host. It refreshes "thinProvisioned" flag and clear the mismatch and the vSAN health alert.