Hello,  One a block has been allocated, it cannot be unallocated currently.   There's is a new SCSI feature coming out called "unmap" which will tell the storage device to unallocate blocks but that isn't universally supported by storage and OS vendors yet.  From the GUI perspective hitting 100% doesn't impact the OS at all.  The OS is keeping track of unallocated LBAs in it's allocation table.  So the array can say 100% used even if the OS says 0% used, go by what the OS says.   If you are using a Thin Provisioned volume and you don't set the limit to 100% when you hit the selected limit, it will put the volume offline.  At which point you either have to change that value or convert it to a classic volume.  Which can be done at any time.  Regards, 
Hi, I was wondering if there is a way to monitor the volume's "In-Use" blocks (ie, within the "In-Use" volume space, how many blocks are actually in-use and how many blocks are no longer in-use).  The reason I ask is because I have large file transfers that tend to increase the "In-Use" space even though the file system shows that it's 43% free (the volume's "In-Use" space is currently at 90% of the volume) and I just want to make sure that it won't max out the volume. Thank you!
Monitoring Volume Blocks Usage