DRBD kernel driver
The DRBD kernel driver presents virtual block devices to the system. It is an important building block of the DRBD SDS. It reads and writes data to optional local backing devices.
The DRBD kernel driver mirrors data writes to one (or multiple) peer(s). In synchronous mode it will signal completion of a write request after it receives completion events from the local backing storage device and from the peer(s).
The illustration on the left shows the path the data takes within the DRBD kernel driver. Please note that the data path is very efficient. No user space components involved. Read requests can be carried out locally, not causing network traffic.