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.

Graduation from the Vienna University of Technology in computer science in 2000. Presentations given at the 6th and 7th Linux Kongress in Germany and at the Second Annual Linux Storage Management Workshop in Miami. Since graduation employment at the biggest provider of professional services in the field of Linux in Austria: CUBiT IT Solutions. Apart from DRBD, author of mergemem (a modification of Linux's memory management system)