Answer inline

On Wed, Apr 5, 2017 at 1:09 AM, Gianluca Cecchi <gianluca.cecchi@gmail.com> wrote:
On Tue, Apr 4, 2017 at 11:49 PM, Elad Ben Aharon <ebenahar@redhat.com> wrote:
Hi Gianluca, 

If you don't have a copy of the template disk on ST2 it means that the VMs were created as deep copy from the template (i.e, they are independent - you can check it in the the 'general' VM sub-tab).

If this is the case then you won't have any problem with detaching ST2.


thanks for reply.
In "general" sub-tab I see

Template: my_template_name (Clone/Independent)

So I should be ok.

Indeed.

But for example I can have ST1 and ST2, create a template with disk in ST1, then a VM from this template again in ST1 and in a second time move the disk of this VM to ST2
In this case what would happen?

VM creation from a template on a storage domain that doesn't have a copy of the template disk can be performed only as deep copy (Clone/Independent). It means that the VM doesn't have any dependency on the template. So you will be able to detach the domain where the VM disk resides.

Is it in this screen when I create a VM that it is decided if deep copy or not as you wrote?
https://drive.google.com/file/d/0BwoPbcrMv8mvdTJMdkNTeF84ckk/view?usp=sharing

Yes. 


What would happen in case I choose "Thin" and not "Clone" in storage allocation part of resource allocation section in the image?

'Thin' means that the VM disk is created as a 'leaf' volume linked to the template disk. It requires the template disk to reside on the storage domain you desire to create the VM disk on. In order to be able to create it in this way you'll first have to copy the template disk to the other storage domain.
 

Also, I noticed that if I create a VM from the blank template the Thin option is checked and both Thin and Clone are greyed out so I cannot change it


Yes, 'Blank' is the default template in the system, clone or thin in this case are not relevant since 'Blank' is just a set of default VM configurations with no disks.
 
Instead if I choose my template, the "Clone" option is marked as default, but I can change to Clone....

Check out ovirt-templates
 
Gianluca