We have a 90GB data volume that free space decreases over time - sometimes
at 2GB per day. When I restart the server, it gains it's free space back.
For eg, it had 6GB free - after restart it had 27GB free.

What's the most likely reason for this...or is it common when volume usage
is over 70%
Is there a command that I can run that free's up the space, without
restarting the server?