DRBD is a high-availability solution for MySQL that combines MySQL, Linux Heartbeat and Distributed Replicated Block Device (DRBD) for a hot-standby solution that synchronously replicates MySQL data between the primary and secondary server.

The key benefit of DRBD over replication is that it enforces data synchronization between the primary and secondary machine, ensuring that the secondary machine has the exact same data as the primary at the time of failover. Replication depends on log shipping and has no guarantee of data synchronization.

DRBD is fully supported by MySQL AB for their enterprise customers.

Further Reference

MySQL and DRBD High Availability Architectures (Whitepaper, Registration required)

DRBD FAQ (MySQL Reference Manual)

An Introduction to High Availability Architectures with MySQL and DRBD (Webinar)

A Quick Tour of DRBD