DRBD

DRBD (or Distributed Redundant 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."

errors
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."
 * "ERROR: unknown cs for drbd0 : BrokenPipe, Update/DUnknown"

run this command to extract useful information.

External resources

 * The DRBD User’s Guide
 * 8.3 change logs
 * 8.4 change logs