Not much, regular glass transitions to crystal quite fast compared to those geological timescales. And who knows what the transition will do to the data stored

Not much, regular glass transitions to crystal quite fast compared to those geological timescales. And who knows what the transition will do to the data stored at these densities. Nothing in the article states what kind of glass is used (which blows the bullshit detector right there). If they use crystalline quartz, it should last indefinitely. If it's regular glass, then 50 years if you're lucky, controlled conditions, etc, etc.