My first DRBD cluster test

Here is my first cluster.  It took me the WHOLE MORNING to figure out (I misunderstood the meaning of the "clone-node-max" property).  Anyhow this is a 4-node active/passive drbd storage cluster.

In this example, only the Primary (pcs "Master") can use the block device at any one time.  The nodes work correctly in that nodes are promoted/demoted as expected when they leave/enter the cluster.

I will have to re-do this entire thing from scratch to make sure I can do it again and keep notes (so many things to remember!).  I will also enable some service here to use the block device: maybe an nfs or LIO iSCSI server or something.

Here are my raw notes and a sample "pcs status" output:

------------RAW NOTES-- SORT IT OUT LATER ----------

pcs resource create block0drb ocf:linbit:drbd drbd_resource=r0
pcs resource master block0drbms block0drb master-max=1 master-node-max=1 clone-max=4
# pcs resource update block0drbms clone-node-max=3 THIS IS WRONG--SHOULD BE 1 BECAUSE ONLY 1 CLONE SHOULD RUN ON EACH NODE (see below later)

pcs resource update block0drbms meta target-role='Started'
pcs resource update block0drbms notify=true

[root@drb3 cores]# systemctl disable drbd
Removed symlink /etc/systemd/system/multi-user.target.wants/drbd.service.

pcs resource update block0drb meta target-role="Started"
pcs resource update block0drb drbdconf="/etc/drbd.conf"

pcs property set stonith-enabled=false
pcs resource update block0drbms clone-node-max=1

pcs resource enable block0drbms



Also (info from the web), fix wrong permissions if needed:

--- chmod 777 some file in /var if needed ---- 

chmod 777 /var/lib/pacemaker/cores

---------- EXAMPLE PCS STATUS OUTPUT --------

[root@drb3 ~]# pcs status
Cluster name: drbdemo
Stack: corosync
Current DC: drb2 (version 1.1.16-12.el7_4.2-94ff4df) - partition with quorum
Last updated: Wed Oct  4 11:38:16 2017
Last change: Wed Oct  4 11:30:36 2017 by root via cibadmin on drb4

4 nodes configured
4 resources configured

Online: [ drb1 drb2 drb3 drb4 ]

Full list of resources:

 Master/Slave Set: block0drbms [block0drb]
     Masters: [ drb2 ]
     Slaves: [ drb1 drb3 drb4 ]

Daemon Status:
  corosync: active/enabled
  pacemaker: active/enabled
  pcsd: active/enabled
[root@drb3 ~]#