We are upgrading controller hardware by moving storage. Original nodes are FAS2620 with internal SATA drives and new nodes are FAS2720 w/o drives.
It's not clear from the official docs if it is possible to move the internal drives from FAS2620 to FAS2720. The documentation says I can move those drive to another disk shelf or convert the original nodes to a shelf.
If you plan to perform the upgrade during an outage window, you can just move the disks between chassis and then assign the disks to the new controller SYSIDs from maintenance mode (with the disk reassign command)
The only doubt was regarding the possibility of moving internal drives from FAS2620 to FAS2720 once the documentation did not cover that scenario. Our SE confirmed internally and it was indeed supported.