DRBD
See the following -
LINBIT Enhances Red Hat Enterprise Linux with Full DRBD Support
Open source high availability powerhouse LINBIT announced full DRBD® support on the Red Hat Enterprise Linux (RHEL) operating system platform this morning. This enhances the world's most widely deployed Linux server platform with the industry's premier storage replication facility - all in a 100% open source software stack. LINBIT, co-based in Vienna, Austria and Beaverton, OR, has been a cornerstone of the Linux high availability community for a decade. DRBD, LINBIT's block-level, synchronous replication solution has defined storage replication on Linux for ten years. It is part of the Linux kernel and is widely deployed across all industries in high availability solutions for databases, storage servers, virtualization and much more.