GitHub user mbertolina added a comment to the discussion: Not able to deploy 
VM: Insufficient un-allocated capacity on StoragePool

Thank you very much for your detailed reply, @RyanP-Testing.

I was able to work around the issue by setting the overprovisioning factor to 2.

However, I don't think this should be the expected storage allocation 
calculation for the volume. Based on my testing, the qcow2 file for the 
template is never expanded.

This is what I observed:

1. When the VM is deployed, the template qcow2 file is copied to the primary 
storage.
2. If the disk service offering used by the VM is **fat**, the original 
template qcow2 file is copied and then expanded, resulting in both the original 
template qcow2 and the expanded qcow2 for the VM volume.
3. If the disk service offering is **thin**, the process is similar, but 
instead of expanding the template qcow2, a new qcow2 is created with the 
template qcow2 as its backing file.

Therefore, in both cases, we have:

* 1 qcow2 file for the template
* 1 qcow2 file for the VM volume

>From what I understand, the maximum possible physical storage consumption in 
>this scenario should be:

**Template physical size + VM volume requested size**

For this particular case:

* Template physical size: **20.81 GB**
* Template virtual size: **1,912.00 GB**
* VM volume requested/virtual size: **1,912.00 GB**

So the expected maximum physical storage requirement should be approximately:

**20.81 GB + 1,912.00 GB ≈ 1.93 TB**

However, CloudStack appears to calculate the required storage as:

**2 × Template virtual size = 2 × 1,912.00 GB ≈ 3.82 TB**

This seems to overestimate the actual possible physical storage consumption by 
using the template's **virtual size** rather than its **physical size**.

Is the design intentionally to always use the virtual/provisioned size for the 
allocated-capacity calculation (regardless of thin/thick and regardless of the 
actual qcow2 physical size on disk)?

Thanks again!

GitHub link: 
https://github.com/apache/cloudstack/discussions/14045#discussioncomment-18316817

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