I've seen issues building indexes on large tables taking excessive amounts of time on anything over 50 GB keys. As I understand it this is do to the sorting...
Mysql does get into trouble with larger datasets, and there is a lot of hacking you need to do. If your talking about single instances of Mysql in a...
As a reply to the large datasets, myisam grew out the data warehouse world and understand it can handle large datasets. However the comment is based on the experience...