You may need to have information replicated between two computers that actually are part of a cluster, in addition to”software” replica mechanisms such as Rsync you can use a product that is stable and included in the standard kernel: DRBD.
DRBD (Distributed Replicated Block Device) is a distributed storage system for the GNU/Linux platform. It consists of a kernel module, several userspace management applications and some shell scripts and is normally used on high availability (HA) clusters. DRBD bears similarities to RAID 1, except that it runs over a network.
DRBD refers to both the software (kernel module and associated userspace tools), and also to specific logical block devices managed by the software. DRBD device and DRBD block device are also often used for the latter.
It is free software released under the terms of the GNU General Public License version 2.