Configuring DRBD

The Pacemaker based MySQL server requires a DRBD resource from which it mounts the /var/lib/mysql directory. In this example, the DRBD resource is simply named mysql:

mysql DRBD resource configuration (/etc/drbd.d/mysql.res). 

resource mysql {
  device    minor 0;
  disk      "/dev/data/mysql";
  meta-disk internal;
  on node1 {
    address ipv4 10.0.42.100:7700;
  }
  on node2 {
    address ipv4 10.0.42.254:7700;
  }
}

This resource uses an underlying local disk (in DRBD terminology, a backing device) named /dev/data/mysql on both cluster nodes, node1 and node2. Normally, this would be an LVM Logical Volume specifically set aside for this purpose. The DRBD meta-disk is internal, meaning DRBD-specific metadata is being stored at the end of the disk device itself. The device is configured to communicate between IPv4 addresses 10.0.42.100 and 10.0.42.254, using TCP port 7700. Once enabled, it will map to a local DRBD block device with the device minor number 0, that is, /dev/drbd0.

Enabling a DRBD resource is explained in detail in the DRBD User’s Guide. In brief, the proper sequence of commands is this:

drbdadm create-md mysql  
drbdadm up mysql  
drbdadm -- --force primary mysql