Remus provides fault tolerance for virtual machines by sending continuous
checkpoints to a backup, which will activate if the target VM fails.

See the website at https://wiki.xen.org/wiki/Remus for details.

Using Remus with libxl on Xen 4.5 and higher:
 To enable network buffering, you need libnl 3.2.8
 or higher along with the development headers and command line utilities.
 If your distro does not have the appropriate libnl3 version, you can find
 the latest source tarball of libnl3 at http://www.carisma.slowglass.com/~tgr/libnl/

Disk replication:
 VMs protected by Remus need to use DRBD based disk backends. Specifically, you
 need a compile and install a custom version of DRBD, that is available publicly
 at https://github.com/rshriram/remus-drbd
 This code is based on DRBD 8.3.11 and uses a new replication protocol (named
 protocol D) for asynchronous disk checkpoint replication. A protected VM's DRBD
 disks on the primary and backup hosts need to be configured to use protocol D
 as the replication protocol. An example resource configuration file can be found
 in the aforementioned github repository.