text: To address this issue, file systems added support for SCSI unmap command, which can be 
  issued after file deletion, and informs the storage system that physical blocks that are used by 
  the removed file should be marked as no longer in use and can be freed up. Modern 
  operating systems issue SCSI unmap commands only to storage that advertises support for 
  this feature. 
  
  V8.1.0 and later releases support the SCSI unmap command on Spectrum Virtualize systems 
  (including SAN Volume Controller, Storwize V5000, Storwize V7000, and FlashSystem 
  V9000). This enables hosts to notify the storage controller of capacity that is no longer 
  required and may be reused or de-allocated, which might improve capacity savings. 
  
  **Note:**For volumes that are outside data reduction pools, the complete stack from the 
  operating system down to back-end storage controller must support unmap to enable the 
  capacity reclamation. SCSI unmap is passed only to specific back-end storage controllers. 
  
  Consider the following points: 
  
  (cid:2) V8.1.2 can also reclaim capacity in data reduction pools when a host issues SCSI unmap 
  commands. 
  
  (cid:2) By default, V8.2.1 does not advertise to hosts support for SCSI unmap. 