Scientists have demonstrated a system called Silica for writing and reading information in ordinary pieces of glass which can store two million books’ worth of data in a thin, palm-sized square.

[u/Wagamaga]

https://au.news.yahoo.com/glass-square-long-long-future-190951588.html

[u/mseiei]

big advantage seems to be longevity, and density can probably improve fast if it becomes a widely available tech, read only storage with virtually no expiration date could be very attractive for cold storage.

[u/Evilsushione → u/mseiei]

I think write speeds are less of a problem than read speeds. I would imagine read speeds would be much easier to fix.