A couple different threat models to consider, hardware failure vs human failure. Things like RAID can effectively cover the hardware failure side and be fully transparent. Human failure is a bit more tricky. There are a number of old expressions about backups but one that’s good to keep in mind is snapshots are not backups. They’re convenient and easy to automate but if the system making them goes kerplooie they’re pretty useless.

A tiered version is good for off device backup, using diff backups routinely to only copy the new or changed data with a periodic full backup.

Cold disks are great but make sure to test them periodically, nothing worse than looking to restore a chunk of data only to find the backup can’t be read.