To share with anyone.    1. from RHEL, # fstrim -v /dir1 (this will send SCSI UNMAP command to SC5020) 2. Expire all snapshots and coalesce last snapshot to Active Space. This will remove all space occupied by snapshots and truncate the whitespace.       
Storage: SC5020 OS: Redhat 6.9 Clustered.  I did 750GB  db restoration, during the job, I had to write and delete backup files on 1.5TB volume. Now the volume is pretty much empty (99%). However, SC5020 shows the volume is 97% full.  It seems as the space emptied out in Red Hat doesn't reflect to SC5020. What is the proper way and command to send space reclamation from Red Hat 6.9 to SC5020?    Thank you in advance. 
SC5020, Red Hat: How to SCSI Unmap to reclaim space?