Configuring the Cluster for a Quorum Device

The node running the quorum device service must be authenticated to the rest of the cluster and must then be added to the cluster. When you add the quorum device service node, you can set configuration options such as which algorithm to use to determine quorum. After the quorum device is added to the cluster you can verify the quorum device status to check that the device is functioning correctly.

Authenticate the quorum device service node to the cluster. On a node within the existing cluster, to authenticate the node named qdev, run:
```
sudo pcs host auth qdev
```
You're prompted for the cluster username and password.
Check that no quorum device is already configured for the cluster. A cluster must never have more than one quorum device configured. On a node within the existing cluster, run:
```
sudo pcs quorum status
```
Note that the output includes membership information:
```
...
Membership information
----------------------
    Nodeid      Votes    Qdevice Name
         1          1         NR node1 (local)
         2          1         NR node2
```
Under the Qdevice column, the value NR is displayed. The NR value indicates that no quorum devices are registered with any of the nodes within the cluster. If any other value is displayed, don't proceed with adding another quorum device to the cluster without removing the existing device first.
Add the quorum device to the cluster. On one of the nodes within the existing cluster, run:
```
sudo pcs quorum device add model net host=qdev algorithm=ffsplit
```
Note that you specify the host to match the host where you're running the quorum device service, in this case named qdev; and the algorithm that you want to use to determine quorum, in this case ffsplit.
Algorithm options are:
- ffsplit: is a fifty-fifty split algorithm that favors the partition with the highest number of active nodes in the cluster.
- lms: is a last-man-standing algorithm that returns a vote for the nodes that are still able to connect to the quorum device service node. If a single node is still active and it can connect to the quorum device service, the cluster remains quorate. If none of the nodes can connect to the quorum device service and any one node loses connection with the rest of the cluster, the cluster becomes inquorate.
See the corosync-qdevice(8) manual page for more information.
Verify that the quorum device is configured within the cluster. On any node in the existing cluster, run:
```
sudo pcs quorum config
```
The output displays that a quorum device is configured and indicates the algorithm that is in use:
```
Options:
Device:
  Model: net
    algorithm: ffsplit
    host: qdev
```
You can also query the quorum status for the cluster by running:
```
sudo pcs quorum status
```
The output displays the quorum status.
```
Quorum information
------------------
Date:             Fri Jul 15 14:19:07 2022
Quorum provider:  corosync_votequorum
Nodes:            2
Node ID:          1
Ring ID:          1/8272
Quorate:          Yes

Votequorum information
----------------------
Expected votes:   3
Highest expected: 3
Total votes:      3
Quorum:           2
Flags:            Quorate Qdevice

Membership information
----------------------
    Nodeid      Votes    Qdevice Name
         1          1    A,V,NMW node1 (local)
         2          1    A,V,NMW node2
         0          1            Qdevice
```
Note that the membership information now displays values A,V,NMW for the Qdevice field. Values for this field can be equal to any of the following:
- A/NA: indicates that the quorum device is alive or not alive to each node in the cluster.
- V/NV: indicates whether the quorum device has provided a vote to a node. In the case where the cluster is split, one node would be set to V and the other to NV.
- MW/NMW: indicates whether the quorum device master_wins flag is set. Any node with an active quorum device that also has the master_wins flag set becomes quorate regardless of the node votes of the cluster. By default the option is unset.