DRBD - Distributed Replicated Block Device

HA Clusters (in Failover configuration) are common practice when a server with mirrored disks (RAID) cannot offer the desired availability for the application. HA Clusters can offer better availability because they can mask failures other than hard disk failures.

DRBD is a device driver for Linux which allows you to build clusters with distributed mirrors, so-called shared nothing clustering. This architecture does not only have the advantage that the physical distance between the two copies of the data can be magnitudes greater than with RAID sets, but it is also (magnitudes) cheaper than clusters with shared disks.

The device reaches between 50% and 98% of the maximum theoretical performance and works well with heartbeat, the HA cluster management software for Linux. We will soon port DRBD to Linux 2.4 and it will then be possible to use it in conjunction with LVM.

At CUBiT IT Solutions DRBD-based clusters have been used in production since June 2000 and overall they have done very well. They are used to mirror various databases (mySQL, Postgresql and a JAVA-based database from Progress) and to form a highly available NFS Server.

You can find more information about DRBD at http://www.complang.tuwien.ac.at/reisner/drbd.