This is an odd issue that I've never seen before and I'm hoping someone out here might be able to help.  We have a VNX 5600 unified system.  I've carved out a 6.5TB file system and presented it as an NFS export to a Linux host for testing.  After doing some testing of place files out there and deleting them we had one more test to run.  Before this test the admin on the system was deleting files and that completed.  The strange thing was that the space from the file system was not showing up as free right away.  There was a delay of approximately 30 minutes before the space showed as free again.  All the other deletes didn't have this delay.  Any thoughts on why this would suddenly occur?