When you perform certain virtual machine management operations, such as create a virtual disk, clone a virtual machine to a template, or migrate a virtual machine, you can specify a format for the virtual disk file.

The following disk formats are supported. You cannot specify the disk format if the disk resides on an NFS datastore. The NFS server determines the allocation policy for the disk.

Thin Provisioned Format

Use this format to save storage space. For the thin disk, you provision as much datastore space as the disk would require based on the value you enter for the disk size. However, the thin disk starts small and at first, uses only as much datastore space as the disk actually needs for its initial operations.


If a virtual disk supports clustering solutions such as Fault Tolerance, you cannot make the disk thin.

If the thin disk needs more space later, it can grow to its maximum capacity and occupy the entire datastore space provisioned to it. Also, you can manually convert the thin disk into thick.

Thick Format

This is the default virtual disk format. The thick virtual disk does not change its size and from the very beginning occupies the entire datastore space provisioned to it. Thick format does not zero out the blocks in the allocated space. It is not possible to convert the thick disk into thin.