It's quite  simple.

For example , you got vm1 with 10GB OS disk that is fully preallocated (actual size is really 10GB).
Now  imagine that you create a snapshot of this vm1 and you download 1GB file from another place.
You will see 2 disk files on the storage domain:
- The original one that was made read-only during the snapshot process
- A new 1GB file that represents the delta (changes between snapshot and current state)

The second file is read-write and if left as is - it will grow up to 10GB (the actual disk of the vm1). When the Virtualization is looking for some data it has to search into 2  places which will reduce performance  a  little bit.If you decide to create another snapshot, the second disk will be made  read-only and another one will be created and so on and so on.

When you delete a snapshot, the disks  will be merged in such way so newer snapshot disks remain, while the rest are merged into a single file.

Restoring  a snapshot is simplest - everything after that snapshot is deleted and the vm1 will use the snapshot disk till you delete (which will merge base disk with snapshot disk) that snapshot.


Best Regards,
Strahil Nikolov

На 2 август 2020 г. 3:53:11 GMT+03:00, jorgevisentini@gmail.com написа:
>Hello everyone.
>
>I would like to know how disk size and snapshot allocation works,
>because every time I create a new snapshot, it increases 1 GB in the
>VM's disk size, and when I remove the snap, that space is not returned
>to Domain Storage.
>
>I'm using the oVirt 4.3.10
>
>How do I reprovision the VM disk?
>
>Thank you all.
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