There are archive grade optical media that are supposed to be good for >100 years. They are not cheap, though.
For normal time scales, use HDDs. I’m not current on unpowered retaining times for bleeding edge drive technology, but there are tests and data sheets that provide answers for different models. Consider copying the data to newer models after 5 to 10 years.
Never, ever consider flash-based media for that. SSDs, SD cards and USB sticks are known to lose content when unpowered, some even after just a year without power.
There are archive grade optical media that are supposed to be good for >100 years. They are not cheap, though.
For normal time scales, use HDDs. I’m not current on unpowered retaining times for bleeding edge drive technology, but there are tests and data sheets that provide answers for different models. Consider copying the data to newer models after 5 to 10 years.
Never, ever consider flash-based media for that. SSDs, SD cards and USB sticks are known to lose content when unpowered, some even after just a year without power.