831
Microsoft develops ultra durable glass plates that can store several TBs of data for 10000 years
(unlocked.microsoft.com)
This is a most excellent place for technology news and articles.
Just out of curiosity, I calculated that the article's (War and Peace * 875,000) claim would net you less than 1TB of storage space (~973GB), assuming it was GZipped (and ~3x that if not).
The most concrete number we have is from another article (also on an official Microsoft page) that claims it's upwards of 7TB.