acroinis true image 2017 compression greyed out
I have True image 2017 and I'm trying to backup 508GB of a 1TB drive through a 3.0 usb interface to a 3TB sata drive.
The back up is taking 18 hours. I checked my setting and compression is greyed out. I normally set it to max which consumes a lot of I5 CPU but makes a small transfer to the backup drive.
Why is compression greyed out on my standalone full backup?