For truly write once read never data tape is the optimal storage method. It is exactly what the LTO standard was designed to do and it does it very well. You can be confident that you will be able to read every bit of data from a 30 year old tape, probably even 50 years old. It has the lowest bit error rate of any technology I am aware of. LTO-9 is better than 1 uncorrectable bit error in 10^20 user bits, which is 1 bit error in 12.5 exabytes. There is also the substantial advantage that tapes on a shelf are completely immune to ransomware. As a sysadmin I get that warm fuzzy feeling when critical data is backed up on a good LTO tape library.