text: **10.3.3 Host SCSI Unmap**
  
  The Spectrum Virtualize system might advertise support for SCSI Unmap to hosts. With it, 
  some host types (for example, Windows, Linux, or VMware) then changes their behavior 
  when creating a file system on a volume, issuing SCSI Unmap commands to the whole 
  capacity of the volume. This causes the system to overwrite the whole capacity with 
  zero-data, and the format completes when all of these writes complete. Some host types run 
  a background process (for example fstrim on Linux), which periodically issues SCSI Unmap 
  commands for regions of a file system that are no longer required. 
  
  Host Unmap commands can increase the free capacity that is reported by the Data Reduction 
  Pool when received by thin-provisioned or compressed volumes. This does not apply to 
  standard storage pools. 
  
  Also, IBM Storwize V7000 sends back-end SCSI Unmap commands to controllers that 
  support them if host unmaps for corresponding blocks are received. 
  
  Host SCSI Unmap commands drive more I/O workload to back-end storage. In some 
  circumstances (for example, volumes on a heavily loaded nearline SAS array), this can cause 