Q: How does the system mirror content from one location on the site to another?

A: eZ Publish has native clustering built in enabling syncing of content between servers. The syncing of multiple servers are automatically managed by eZ Publish where the different servers will be identical. The databases (MySQL) can also be configured in a replication environment. This can be used to create a load balanced environment with fail-over and also a hot-backup for recovery in case of a crash of the main servers.
You can also configure cold backups that typically are done incrementally and periodically e.g. every night. Both approaches can be used at the same time.