Just wanted to give folks a heads up on an issue that a colleague of mines recently identified when provisioning Virtual Appliances (OVF/OVA) onto a VSAN datastore when using the vSphere Web Client. He found that regardless of the VSAN Storage Policy that was selected, whether it is the default VSAN Storage Policy or a custom one, the Virtual Appliance will always be Thick provisioned.

This behavior only occurs when using the vSphere Web Client and is not observed when using either the vSphere C# Client or the ovftool CLI. My understanding of the issue is that there are two ways in which a VM can get provisioned as Thin. The "old" method which was to explicitly specify the disk allocation type (Thin vs Thick) and the "new" method which uses VM Storage Policies. To ensure that we maintain backwards compatibility for older clients, if a client specifies Thick provisioned, it would actually override the VM Storage Policy even if the Object Space Reservation capability was set to 0 (Thin provisioned). Since you can no longer specify the disk allocation type in the vSphere Web Client, the default behavior is to not Thin provision and hence the current Thick provisioning result even though the default VSAN Storage Policy has OSR set to 0.

Note: When referring to Thick provisioned in VSAN (proportionalCapacity = 100), It is defined as provisioned Thin with a reservation so there is a guarantee that space is available for the object. It is not accurate to compare this to Zeroed Thick or Eager Zeroed Thick in the VMFS/NFS world as VSAN is an Object Store.

Engineering has already been engaged and is currently investigating the issue. We have also asked for a VMware KB to be published, so hopefully once that goes up, folks can subscribe to that for more details and updates.

In the meantime, since it is actually pretty difficult to see if you have been affected by issue, I have created a simple PowerCLI script called Get-VSANPolicy.ps1 which will allow you to quickly scan through your VM(s) to identify whether you have any VMs that have been Thick provision residing on a VSAN Datastore. You can either get all VMs by piping Get-VM * or a specific set of VMs into the script.

The following example retrieves all VMs that start with "Photon-Deployed-From-*" and extracts their current VSAN VM Storage Policy for both VM Home and individual VMDKs. Here, we can see that both VMs are using the default VSAN VM Storage Policy.

Get-VM "Photon-Deployed-From-*" | Get-VSANPolicy -datastore "vsanDatastore"

Lets now only search for VMs that have been Thick provisioned by using the -thick option and setting that to true. Here we can see that the OVF we provisioned through the vSphere Web Client is the only VM listed.

Get-VM "Photon-Deployed-From-*" | Get-VSANPolicy -datastore "vsanDatastore" -thick $true

If we want to get more details on the underlying VM Storage Policy that was applied, we can also specify the -details option to true. Here we can clearly see that the 2nd VM has proportionalCapacity=100 which means Thick provision.

Get-VM "Photon-Deployed-From-*" | Get-VSANPolicy -datastore "vsanDatastore" -thick $true -details $true

Luckily, the fix is quite easy thanks to Paudie O'Riordan who found out that it was as simple as just re-applying the VSAN VM Storage Policy! (Policy Based Management FTW!) This means there is no need to perform unnecessary Storage vMotions to be able to convert the VM from Thick to Thin, it is literally a couple of clicks in the UI.

UPDATE (07/15/16) - Thanks to reader Jose, it looks like using the vSphere Web Client to re-apply the VSAN VM Storage Policy will correctly apply the policy to the VM/VMDKs, but does not reclaim the underlying storage. It is recommended that you use the PowerCLI script below to re-apply the policy which will then properly reclaim the underlying storage and will properly reflect the storage utilization.

As with anything, I still prefer Automation and with that, I have created a secondary script to help with the remediation. This is also a PowerCLI script called Set-VSANPolicy.ps1 which accepts a list of VMs and the name of the VSAN VM Storage Policy that you wish to re-apply.

Here is an example of running the script and remediating two VMs that contains multiple VMDKs:

Set-VSANPolicy -listofvms $listofvms -policy $vsanpolicy

If you now re-run the first script, you should see that you no longer have VMs that are provisioned Thick anymore (this may take some time depending on the size of your VMs).