Relational SQL databases, which have been around since the 1980s, historically ran on mainframes or single servers—that’s all we had. If you wanted the database to handle more data and run faster, you had to put it on a bigger server with more and faster CPUs, memory, and disk. In other words, you turned to vertical scalability or “scale up.” Later on, if you needed the ability to fail-over to improve availability, you could collocate a hot back-up server with the active server in an “active-passive” cluster, typically with shared storage.
