[ovirt-users] Clone, template, pools : how does it uses disk space ?

Alexis HAUSER alexis.hauser at telecom-bretagne.eu
Mon May 23 09:50:48 UTC 2016


I would like to know what happens to storage when using the different method of cloning or generating VMs using templates / pools.
I'd like to know also in what case VM and virtual disks are totally independent and in what case they are not.
Sadly the RHEV documentation doesn't really provide these informations and I don't find any explicit informations about it.

For example, when making a VM from template, using pre-allocated disk option, for a 50GB Virtual disk, it only uses 3GB on the physical disk.
Another example, when making a pool of 10 VMs, based on a VM with a 50 GB virtual disk, only 2GB more space is used on the physical disk.
What is exactly done when this happens ?

Here are the case I would like to have informations about (physical storage, and independence of VMs) :
- using simple "clone function"
- making VM from template with "clone" mode
- making VM from template with "thin" mode
- making VM in pools

Is there modes calculating only the difference from the original VM, and other modes copying totally the informations from the virtual disk from the original VM ?

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