In RHEV by default, virtual machines created from templates use thin provisioning. In the context of templates, thin provisioning of vm means copy on write (aka linked clone or difference disk) rather than a growing file system that only takes up the storage space that it actually uses (usually referred to as thin provisioning). All virtual machines based on a given template share the same base image as the template and must remain on the same data domain as the template.

You can however specify to deploy the vm from template as clone - which means that a full copy of the vm will be deployed. When selecting to clone you can then select thin (sparse) or pre-allocated provisioning of the full clone. Deploying from template as clone results in independence from the base image but space savings associated with using copy on write approaches are lost.

A virtual disk with a preallocated (RAW) format has significantly faster write speeds than a virtual disk with a thin provisioning (Qcow2) format. Thin provisioning takes significantly less time to create a virtual disk. The thin provision format is suitable for non-IO intensive virtual machines.