DRBD

DRBD allows transparent and reliable replication of data between hosts - basically a RAID1 service that runs between machines.

To make this tie into the rest of the setup, drbd has its own mountpoint, /drbd, and the various cluster services are underneath there.

The DRBD implementation we're using uses Bind Mounts to put everything in it's proper places.

DRBD volumes are using LVM, to ease management pain.

There is one LVM volume for each service: