High Availability with DRBD
As more and more mission-critical applications move on the Internet, providing highly available services becomes increasingly important. DRBD software is a distributed replicated storage system for the Linux platform. It is implemented as several userspace management applications and some shell scripts and is normally used on high availability (HA) computer clusters.
Replication occurs in real time and continuously, while applications make changes in the data on the device.
The application programs that store their data on the mirrored device are unaware of the fact that the data is in stored on multiple computers.
With synchronous mirroring, the write completion notification to a writing application is given only after the write process has been carried out on both computer systems.
With asynchronous mirroring, the write completion notification to a writing application is given when the write has completed locally, but before the write has propagated to the peer system.