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

> I tested with a thin disk service offering and Overprovisioning factor=1 on 
> primary storage and got the same error when allocating the space for the VM

@mbertolina 
Let me give you an example:

- Create a 100 GB ROOT disk. The actual physical usage is only 5 GB (for the 
operating system).
- Create a 100 GB DATA disk. The actual physical usage is 0 GB because it is 
empty.

In this case, the total allocated size is 200 GB, but only 5 GB is actually 
used on the physical storage pool.

If the storage pool size is 200 GB:

- With an overprovisioning factor of 1, you cannot create any new volumes 
because the total allocated capacity has already reached 200 GB (200 × 1), even 
though only 5 GB is physically used.
- With an overprovisioning factor of 5, the total allocated capacity is 1,000 
GB (200 × 5), so you can still create several volumes. However, there is a risk 
that the virtual disks eventually consume their full 100 GB each, which could 
result in the physical storage pool becoming full.

This is the trade-off with overprovisioning: a lower factor provides more 
protection against the storage pool becoming full, but may leave physical 
capacity underutilized. A higher factor allows you to make better use of the 
physical storage, but increases the risk of running out of physical space if 
the volumes actually consume their allocated capacity.



GitHub link: 
https://github.com/apache/cloudstack/discussions/14045#discussioncomment-18268624

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