Piracy: ꜱᴀɪʟ ᴛʜᴇ ʜɪɢʜ ꜱᴇᴀꜱ

Contrary to what people suggested, I would advise against optical discs or tapes and would go with HDDs you check every few months. They don't rot like optical media, the only thing you have to worry about are the motor spindles getting stuck and other mechanical failures.

It will also be the cheapest option. With tapes you need expensive drives and they change the version every few years. Tapes only are better if you store hundreds or thousands of TiB of data.

Which data so you want to save? Mostly games and media? If so, consider giving them to your friends and family to copy and enjoy, which some people call a 'friend backup'.

There’s a rule I was always told in A+. Either a hard drive is going to last you less than a year or it’s gonna last you five. Usually any problems with a hard drive you’ll see right away. However after the third year is when I’d start checking the drive. There are tools out there that can let you know when a drive is in the caution level and that’s when you should think about replacement. I’ve had hard drives like one I have to replace soon last me eight years with constant use as a Plex drive.

Discs aren't very suitable for long term storage. Really the only thing truly suited for long term storage of digital media is archival tape. Which isn't cheap or accessible. The only accessible solution is to keep it alive in a raid and keep rebuilding as disks fail over the years.