I have read the documentation on using datactl but have not seen any documents on what do back up and what to restore. If the SD fails, what do I do? If the SSD fails, what is needed. It is clear how to restore on either the SD or SSD. I do not know how to restore the split?
There are several excellent tutorials for setting up the pi to boot from USB. I did not see a difference using the official install method of boot from SD and everything else on SSD. I found if your hardware is compatible you can boot directly from the SSD. I still have issues on my system with every HA OS after 5.4. The system freezes after many hours. Lots of open Github issues since November 2020. I have since moved to Debian with HA supervisor. No issues in over a month. Kong Who wrote a very good tutorial on this.