Using Cloudmin on srv1, I've tried to clone ns2 on srv2 to either srv2 or to srv3, both of which fail with insufficient storage errors:
"Creating clone of KVM system ns2.cloud.virtualmin.com named ns4 ..
.. failed : The host system srv2.cloud.virtualmin.com is not suitable for this clone : Only 8.95 GB disk space would be free after creating this system, but the minimum is 10 GB"
In this case, I found that having a directory filled in on the Host Systems page for srv2 would cause that particular check to test against the filled in directory, even though the logical volume option was selected and the VM has 800+GB of free space. So, in this case I think it's just a bug in how that form is handled maybe. It seems like it shouldn't need to be emptied if the directory option isn't selected.
And for srv3:
Creating clone of KVM system ns2.cloud.virtualmin.com named ns4 ..
.. failed : The host system srv3.cloud.virtualmin.com is not suitable for this clone : Only 38.55 GB disk space would be free after creating this system, but the minimum is 100 GB
In the case of creating the clone on srv3, I have no idea why it failed. That system has tons of space on its LV that's assigned for storage, and the Host Systems page reports that correctly.