Seagate already have 3TB drives in the marketplace. However, they are packaged inside FreeAgent GoFlex enclosures.
http://www.seagate.com/www/en-us/products/external/external-hard-drive/desktop-hard-drive/
According to this review ...
http://www.crunchgear.com/2010/07/01/hands-on-the-seagate-freeagent-goflex-desk-3tb-external-hard-drive/
... the drive is a 7200 RPM, 3TB, Barracuda XT, model ST33000651AS.
Here is a close-up of the label:
http://www.crunchgear.com/wp-content/uploads/2010/07/freeagent-goflex-desk-3tb-2.jpg
According to HD Tune, the average read performance is 130 MB/s.