Howtoforge posted a tutorial about setting up network RAIF1 with DRBD on Debian Squeeze

This tutorial shows how to set up network RAID1 with the help of DRBD on two Debian Squeeze systems. DRBD stands for Distributed Replicated Block Device and allows you to mirror block devices over a network. This is useful for high-availability setups (like a HA NFS server) because if one node fails, all data is still available from the other node.

  Setting Up Network RAID1 With DRBD On Debian Squeeze