This article clarifies when virtual disk provisioning type can change on ESX hosts. (Disk provisioning type is sometimes called disk allocation type.)
Note: Virtual disk provisioning types are "thin", "thick" or "lazy zeroed thick" (LZT), and "eager zeroed thick" (EZT).
For more details, refer: Virtual Disk Provisioning Policies
Symptoms:
- After creating, migrating or cloning a virtual disk, you notice the provisioning type of the disk does not match what you selected in the UI or specified in the API call.
- After a VM has been running for a period of time, you notice the provisioning type of a disk attached to that VM has changed from thin or thick to eager zeroed thick.
- After snapshotting, restoring, or backing up a VM, you notice the provisioning type of a disk attached to that VM has changed.
- After inflating, growing, shrinking, encrypting, or otherwise modifying a virtual disk, you notice its provisioning type has changed.
Note: The current provisioning type of a disk can be seen in the "Edit Settings" tab or the "VM Hardware" tile in the HTML5 UI.