My concern about my own backup strategy (which, for Photos, is exactly the same as yours) is that I don't have a system in place that notifies me if files get corrupted or randomly deleted, and I'm not sure how I would go about implementing something like that. Any ideas?
I use a synology for TM (raid 1) and it uses btrfs which has checksums to prevent bitrot. Either that or something running ZFS would be the obvious options:
