> And what if it gets scratched? What is the error tolerance? At that density, a single speck of dust could have dramatic implications... My understanding is t

> And what if it gets scratched? What is the error tolerance? At that density, a single speck of dust could have dramatic implications... My understanding is that it doesn't matter. The data is embedded three dimensionally in glass. Assuming there was some small margin of glass around the patterned region, you could simply grind / polish off the scratches. Of course if you scratched it deep enough to destroy the data region then you'd be out of luck, but this can be made arbitrarily difficult. Furthermore, you can arbitrarily scale error tolerance with error correcting encodings; data can be distributed, such that damage in one or a few areas is still available elsewhere, similar to RAID 5 and 6.