★ VM disk size modification

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The VM disk provision mode is thin, which also allows to modify the disk storage of the VM, but why can"t it be modified to the sum of the allocated disk storage plus the capacity of the storage pool where the VM is located?

When you allocate 1T to a VM and the disk provision mode is thin, how much storage the VM uses is displayed (173.82GB used as shown below), and the available storage of the storage pool where VM is located is including the unused storage space of the VM, so it cannot be modified to the sum of the original storage space plus the capacity of the storage pool where the VM is located. 

The mechanism for increasing the VM disk storage is that the maximum change can only be made to the sum of the available storage of the storage pool where the VM is located and the capacity already used by the VM, and does not include the capacity originally set by the VM, for example, as shown in the figure below, the maximum storage of the VM can only be changed to approximately 1.49 (1.32T plus 173.82G).