The Archive currently has about 46 Petabytes of content ("bytes archived"), and over 120 PB of raw disk capacity; the difference is due to data replication, "currently filling" storage, non-storage infrastructure, etc.

We save a lot on web content storage by de-duplicating "revists" when the page hasn't changed. This works out to save a whole lot for content like jQuery served from a common CDN URL; it doesn't work well when there is a page counter or any trivial changing content on a page.

If you are interested in the storage back-end, it's actually pretty simple: HTTP requests/responses are concatenated and compressed in WARC files (sort of like .tar.gz) that get stored on regular old ext4 filesystems. An index of "what URL captures are in what WARC files on what servers" is continuously generated in the form of, basically, a giant sorted (and shareded) .tsv file; replay requests on web.archive.org look up the URL and timestamp and get a reference to a machine, file, and file offset, and make an HTTP 1.1 range request for the content in question. There are a bunch of other details, like checking robots.txt status, but the core design is super simple, cheap, and (relatively) easy to operate at scale.

Apart from web crawl content (including, these days, "heavy" video content which is difficult to de-dupe), we have a large amount of live recorded TV, scanned books (raw photos), etc.

(I currently work at IA)