DRBD (or Distributed Replicated Block Device) is a network block device that provides reliability when storing data across multiple network nodes.
From the kernel documentation:
DRBD is a shared-nothing, synchronously replicated block device. It is designed to serve as a building block for high availability clusters and in this context, is a "drop-in" replacement for shared storage. Simplistically, you could see it as a network RAID 1.
Device Drivers ---> Block devices ---> <*> DRBD Distributed Replicated Block Device support
emerge --ask sys-cluster/drbd
This package installs the userland utilities to interact with, and control DRBD. Also known as drbdsetup and drbdadm.
"ERROR: unknown cs for drbd0 : BrokenPipe, Update/DUnknown"
This error means connection state has a problem, link needs fixing, or drbd version updating. Upstream states "we had some issues with discarding the first successful connection and getting in a connect/brokenpipe loop."
Run this command to extract useful information.