Installing and configuring a quorum device

You can install and configure a quorum device for a Db2® instance that is running on a Pacemaker-managed Linux cluster.

Before you begin

The quorum device requires an extra host that other hosts in the cluster can connect to via a TCP/IP network. However, the quorum device host does not need to be configured as a part of the cluster. You do not need to install the Db2 software for this operation; the only requirement for the quorum device to function is to install a singular or multiple corosync-qnetd RPMs on it.

Note: The corosync-qnetd RPMs provided also contain debug versions. When you install corosync-qnetd RPMs, you can choose to install the debug version, however, it is not required. The corosync-qnetd RPM must be the version validated by Db2 and downloaded from the IBM site.
Note: It is recommended that a quorum device be run on a different physical network at the same site as the cluster that uses the quorum device. Ideally, the quorum device host should be in a separate rack than the main cluster, or at least on a separate PSU and not on the same network segment as the corosync ring or rings.

About this task

Having a reliable quorum mechanism is essential to a highly available cluster. A quorum device is required for Mutual Failover (MF) and High Availability Disaster Recovery (HADR) instances. For pureScale and Data Partitioning Feature (DPF) configurations, a quorum device is required if the cluster contains an even number of nodes. Alternatively, support for running a 2-node pureScale cluster configuration without a quorum device is permitted since the tie-breaker mechanism is provided by the cluster file system.

The following placeholders are used in the command statements throughout this procedure. These represent values that you can change to suit your organization:
  • <platform> Use linuxamd64, linuxppc64le, or linux390x64.
  • <OS_distribution> is your Linux operating system (OS). Use either RHEL or SLES.
  • <architecture> is the chipset you are using. Use x86_64, ppc64le, or s390x.

Procedure

  1. On each node in the cluster, ensure that the corosync-qdevice package is installed with the following command:
    rpm -qa | grep corosync-qdevice
  2. If the corosync-qdevice package is not installed, install it:
    • On Red Hat Enterprise Linux (RHEL) systems:
      dnf install <Db2_image>/db2/<platform>/pcmk/Linux/rhel/<architecture>/corosync-qdevice*
    • On SUSE Linux Enterprise Server (SLES) systems:
      zypper install --allow-unsigned-rpm<Db2_image>/db2/<platform>/pcmk/Linux/sles/<architecture>/corosync-qdevice*
  3. On the quorum device host, install the Corosync QNet software:
    • On RHEL systems:
      dnf install<Db2_image>/db2/<platform>/pcmk/Linux/rhel/<architecture>/corosync-qnetd*
    • On SLES systems:
      zypper install --allow-unsigned-rpm<Db2_image>/db2/<platform>/pcmk/Linux/sles/<architecture>/corosync-qnetd*
  4. As the root user, set up the QDevice from one of the cluster nodes.
    <Db2_install_path>/bin/db2cm -create -qdevice <hostname>
    Important: To run the db2cm utility as the root user, ensure the DB2INSTANCE environment variable is set to the instance owner.
    Note: Due to corosync requirements, you must configure passwordless root secure shell (SSH) access and enable secure copy protocol (SCP) for the cluster nodes and qdevice host. Ensure that you are able to use root passwordless SSH between all hosts, as well as locally on the current host. Passwordless root SSH is only needed for initial configuration, and further configuration changes. Passwordless root SSH is not needed for continued QDevice work.
  5. Run the following corosync command on the cluster nodes to verify that the quorum was setup correctly.
    corosync-qdevice-tool -s
    Alternatively, as root user, run the db2cm -status on the cluster nodes to verify that the quorum device is configured correctly.
  6. Run the following corosync command on the quorum device host to verify that the quorum device is running correctly:
    corosync-qnetd-tool -l

Examples

The following examples show the command syntax and output from running the corosync-qdevice-tool command, the db2cm -status command and the corosync-qnetd-tool command to verify a quorum device has been correctly configured. Alternatively, Alternatively, as root user, run db2cm -status on the cluster nodes to verify that the quorum device is configured correctly. The corosync-qnetd-tool command is run on the quorum device host to verify that the quorum device is running correctly (see step 6). In the examples, frizzly1 is the name of the quorum device host.

All Configurations

For all availability configurations, the output from the db2cm -status command will contain the following section if the quorum device is configured correctly on the current host. This command should be run on all cluster nodes.
QDevice Information:
 * Connected: [ frizzly1:5403 ]

HADR and MF

On all cluster nodes:

[root@cuisses1 ~]# corosync-qdevice-tool -s
Qdevice information
-------------------
Model: Net
Node ID: 1
Configured node list:
0 Node ID = 1
1 Node ID = 2
Membership node list: 1, 2
Qdevice-net information
----------------------
Cluster name: hadom
QNetd host: frizzly1:5403
Algorithm: LMS
Tie-breaker: Node with lowest node ID
State: Connected

On the quorum device host:

[root@frizzly1 ~]# corosync-qnetd-tool -l
Cluster "hadom":
Algorithm: LMS
Tie-breaker: Node with lowest node ID
Node ID 2:
Client address: ::ffff:9.21.110.42:55568
Configured node list: 1, 2
Membership node list: 1, 2
Vote: ACK (ACK)
Node ID 1:
Client address: ::ffff:9.21.110.22:51400
Configured node list: 1, 2
Membership node list: 1, 2

pureScale and DPF

On all cluster nodes:

[root@cuisses1 ~]# corosync-qdevice-tool -s
Qdevice information
-------------------
Model: Net
Node ID: 1
Configured node list:
 0 Node ID = 3
 1 Node ID = 4
 2 Node ID = 2
 3 Node ID = 1
Membership node list: 1, 2, 3, 4

Qdevice-net information
----------------------
Cluster name: db2domain
QNetd host: frizzly1:5403
Algorithm: Fifty-Fifty split
Tie-breaker: Node with lowest node ID
State: Connected
On the quorum device host: 
[root@frizzly1 ~]# corosync-qnetd-tool -l
Cluster "db2domain":
 Algorithm: Fifty-Fifty split (KAP Tie-breaker)
 Tie-breaker: Node with lowest node ID
 Node ID 1:
 Client address: ::ffff:9.30.119.73:36200
 Configured node list: 3, 4, 2, 1
 Membership node list: 1, 2, 3, 4
 Vote: ACK (ACK)
 Node ID 2:
 Client address: ::ffff:9.30.182.240:37932
 Configured node list: 3, 4, 2, 1
 Membership node list: 1, 2, 3, 4
 Vote: ACK (ACK)
 Node ID 3:
 Client address: ::ffff:9.30.183.140:51636
 Configured node list: 3, 4, 2, 1
 Membership node list: 1, 2, 3, 4
 Vote: ACK (ACK)
 Node ID 4:
 Client address: ::ffff:9.30.160.40:52388
 Configured node list: 3, 4, 2, 1
 Membership node list: 1, 2, 3, 4
 Vote: No change (ACK)