Migration and upgrade
I've been using mysql slaves for years, and it is not only easy to set up, but also a perfect candidate as a readonly mirror of the wiki.
And the slave can be set as master anytime, making the mirror the main wiki when the original one goes down. This ensures zero downtime if set up automatically.
Anyway, this is not a replacement of monthly backup. If a hacker managed to run drop db, the slave will also be destroyed.