Here's how I got my root fs over to the USB SSD:
fdisk to create a single linux partition on the SATA drive
2 - Changed
/boot/cmdline.txt to reference
3 - Reboot
4 - Used
e2label to remove the ROOT label from the old SDcard partition and added ROOT to the new partition on
5 - Edited
/etc/fstab to add
LABEL=ROOT / ext4 defaults,noatime 0 0.
6 - Rebooted
All set!! Only thing I could still do is remove the partition from the sd card if I wanted to. Might even set up a nightl rsync to copy the SSD back to the SDcard as a back up but probably not worth it.