I need to upgrade an old Debian 6 to the latest release: the server host mail and samba NT4 domain for a small office. Everything, including /boot partition, is inside a software raid. What is the best choice to run the upgrade and be able to recover in case of system not working? Is it possible to remove one disk of the RAID1, do the upgrade, check everything is OK then reconnect the disk and leave it sync all the night? In case of failure I'll start the system with the old disk and after connect the "upgraded" one to let it resync back.
Do you see any issue with this procedure? Do you have other hints?