text: IBM Storwize V7000 allocates provisioning_group_id, which is the 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: 
  
  – 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 the 
  physical storage that is in use much like an external array. 
  
  The physical_capacity and physical_free_capacity parameters belong to the MDisk’s 
  provisioning group. They 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. 