IBM SAN Volume Controller allocates  provisioning_group_id , which is an identifier for  the provisioning group that is affiliated with the MDisk. A provisioning group is an object  that represents a set of managed disks that share physical resources. This is represented  differently depending on the back-end storage, as shown in the following examples: The parameters  physical_capacity  and  physical_free_capacity  belong to the MDisk’s  provisioning group and indicate the total physical storage capacity and formatted available  physical space in the provisioning group that contains this MDisk. Note:  It is not recommended to create multiple storage pools out of a MDisks in a single  provisioning group. 458  Implementing the IBM System Storage SAN Volume Controller with IBM Spectrum Virtualize V8.2.1 – A9000: The entire subsystem forms one provisioning group. – Storwize V7000: The storage pool forms a provisioning group, which allows more than  one independent provisioning group in a system. – RAID with compressing drives: An array is a  provisioning group that presents physical  storage in use much as an external array.