Not -really- all that big by today's standards but we don't know exactly how big it was. I've seen numbers from 50,000 to 400,000 scrolls of unknown length.

A modern library, even of modest size has 400,000 books. I work for a top 50 University's library and we have about 1.2 Million. "Big" collections are frequently over 3 million. Here's a handy list of American Libraries by collection size: http://www.ala.org/tools/libfactsheets/alalibraryfactsheet22