Archive disks such as USB external drives that can be stored elsewhere. They are very compact and hold a lot of data. A 4TB USB external 3.5" hard drive should

Archive disks such as USB external drives that can be stored elsewhere. They are very compact and hold a lot of data. A 4TB USB external 3.5" hard drive should be very suitable. Hard drives are very stable and readable decades later as a general rule. Much better than the CDROMs and DVDs that were touted as 'permanent' when they first arrived, only to be shown as very impermanent in practice.