When is there going to be an automatic procedure for this? Like a "prepare drive for removal" button, a "prepare drive for decommissioning" button and then also a "securely erase decommissioned drive" button. Is there a feature request that is already being worked on?
At this point it could alert you that you have useful data on the "decommissioning" drive and do this for you... (and by doing this for you, I mean moving the data to free space on the array for you, maintaining data safety)