This is a draft document that was built and uploaded automatically. It may document beta software and be incomplete or even incorrect. Use this document at your own risk.

Jump to content
Configuring QDevice and QNetd in an Existing High Availability Cluster
SUSE Linux Enterprise High Availability 16.0

Configuring QDevice and QNetd in an Existing High Availability Cluster

Publication Date: 24 Oct 2025
WHAT?

How to use the CRM Shell to configure QDevice and QNetd in a High Availability cluster that is already installed and running.

WHY?

QDevice and the arbitrator QNetd participate in quorum calculations in a split-brain scenario. This allows the cluster to sustain more node failures than the standard quorum rules allow.

EFFORT

Configuring QDevice and QNetd in an existing cluster only takes a few minutes and does not require any downtime for cluster resources.

GOAL

Help the cluster make quorum calculations more easily. This is recommended for clusters with an even number of nodes, especially two-node clusters.

REQUIREMENTS
  • An existing SUSE Linux Enterprise High Availability cluster.

  • An additional SUSE Linux Enterprise Server to run QNetd.

  • We recommend having the cluster nodes reach the QNetd server via a different network than the one Corosync uses. Ideally, the QNetd server should be in a separate rack from the cluster, or at least on a separate PSU and not in the same network segment as the Corosync communication channels.

1 What are QDevice and QNetd?

When communication fails between one or more nodes and the rest of the cluster (a split-brain scenario), a cluster partition occurs. The nodes can only communicate with other nodes in the same partition and are unaware of the separated nodes. A cluster partition has quorum (or is quorate) if it has the majority of nodes (or votes). This is determined by quorum calculation. Quorum must be calculated so the non-quorate nodes can be fenced.

QDevice and QNetd participate in quorum calculations in a split-brain scenario. QDevice runs on each cluster node and communicates with an arbitrator, QNetd, to provide a configurable number of votes to the cluster. This allows the cluster to sustain more node failures than the standard quorum rules allow. We recommend using QDevice and QNetd for clusters with an even number of nodes, and especially for two-node clusters.

1.1 Components

QDevice (corosync-qdevice)

QDevice runs together with Corosync on each cluster node. It communicates with the arbitrator QNetd to provide a configurable number of votes to help with quorum calculation.

QNetd (corosync-qnetd)

QNetd is an arbitrator that provides a vote to the QDevice service running on the cluster nodes. The QNetd server runs outside the cluster, so you cannot move cluster resources to this server. QNetd can support multiple clusters if each cluster has a unique name.

Algorithms

QDevice supports different algorithms to determine how votes are assigned. Fifty-fifty split is helpful for clusters with an even number of nodes. Last man standing is helpful for clusters where only one active node needs to remain quorate.

Heuristics

QDevice supports a set of commands (or heuristics) that run when the cluster services start (or restart), when the cluster membership changes, and when nodes connect to the QNetd server. Optionally, you can also configure the commands to run at regular intervals. The result is sent to QNetd to help with the quorum calculation. Heuristics can be written in any programming language.

Tiebreaker

This is used as a fallback if the cluster partitions are equal even after the heuristics results are applied. The tie-breaker vote can be configured to go to the node with the lowest node ID, the highest node ID, or a specific node ID.

1.2 Benefits

  • Clusters with an even number of nodes can make quorum calculations more easily.

  • The cluster can sustain more node failures than the standard quorum rules allow.

  • You can write your own heuristics scripts to affect votes. This is especially useful for complex setups.

  • Two-node clusters can use diskless SBD if QDevice is also configured.

  • One QNetd server can provide votes for multiple clusters.

  • QNetd can work with TLS for client certificate checking.

1.3 For more information

For more information, see the man pages corosync-qdevice and corosync-qnetd.

2 Setting up the QNetd server

QNetd is an arbitrator that provides a vote to the QDevice service running on the cluster nodes. The QNetd server runs outside the cluster, so you cannot move cluster resources to this server. QNetd can support multiple clusters if each cluster has a unique name.

By default, QNetd runs the corosync-qnetd daemon as the user coroqnetd in the group coroqnetd. This avoids running the daemon as root.

Requirements
  • SUSE Linux Enterprise Server is installed and registered with the SUSE Customer Center.

  • You have an additional registration code for SUSE Linux Enterprise High Availability.

  • We recommend having the cluster nodes reach the QNetd server via a different network than the one Corosync uses.

Perform this procedure on a server that is not part of the cluster:

  1. Log in either as the root user or as a user with sudo privileges.

  2. Enable the SUSE Linux Enterprise High Availability extension:

    > sudo SUSEConnect -p sle-ha/16.0/x86_64 -r HA_REGCODE
  3. Install the corosync-qnetd package:

    > sudo zypper install corosync-qnetd

    You do not need to manually start the corosync-qnetd service. It starts automatically when you configure QDevice on the cluster.

The QNetd server is ready to accept connections from a QDevice client (corosync-qdevice). Further configuration is handled by crmsh when you connect QDevice clients.

3 Connecting QDevice to the QNetd server

QDevice runs together with Corosync on each cluster node. It communicates with the arbitrator QNetd to provide a configurable number of votes to help with quorum calculation.

This procedure explains how to configure QDevice after the cluster is already installed and running, not during the initial cluster setup.

Important
Important: Cluster restart might be required

The setup script checks if a cluster restart is required and whether it is safe to do so automatically. If any non-STONITH resources are running, the script warns you to restart the cluster services manually. This allows you to put the cluster into maintenance mode first to avoid resource downtime. However, be aware that the resources will not have cluster protection while in maintenance mode.

Requirements
  • An existing High Availability cluster is already running.

  • The latest corosync-qdevice package is installed on all nodes.

  • The latest corosync-qnetd package is installed on the QNetd server.

  • To connect to the QNetd server as a sudo user: The user must have passwordless sudo permission.

  • To connect to the QNetd server as the root user: Passwordless SSH authentication must be configured between the nodes and the QNetd server.

Perform this procedure on only one cluster node:

  1. Log in either as the root user or as a user with sudo privileges.

  2. Run the QDevice stage of the cluster setup script:

    > sudo crm cluster init qdevice
  3. Confirm with y that you want to configure QDevice and QNetd.

  4. Enter the IP address or host name of the QNetd server, with or without a user name:

    • If you include a non-root user name, a later step will prompt you for the user's password and the script will configure passwordless SSH authentication from the nodes to the QNetd server.

    • If you omit a user name, the script defaults to the root user, so passwordless SSH authentication must already be configured for the nodes to access the QNetd server.

    For the remaining fields, you can accept the default values or change them as required:

  5. Accept the proposed port (5403) or enter a different one.

  6. Choose the algorithm that determines how votes are assigned. The default is ffsplit.

    • ffsplit (fifty-fifty split): If the cluster splits into two even partitions, one of the partitions gets the vote based on the results of heuristics checks and other factors. This algorithm is helpful for clusters with an even number of nodes.

    • lms (last man standing): If only one remaining node can still communicate with the QNetd server, that node gets the vote. This algorithm is helpful for clusters where only one active node needs to remain quorate.

  7. Choose the method to use when a tie-breaker is required. The default is lowest.

    • lowest: The node with the lowest node ID gets the vote.

    • highest: The node with the highest node ID gets the vote.

    • Alternatively, you can enter a specific node ID. The designated node always gets the vote.

  8. Choose whether to enable TLS for client certificate checking. The default is on.

    • off: TLS is not required and should not be tried.

    • on: Attempt to connect with TLS, but connect without TLS if it is not available.

    • required: TLS is mandatory, so QDevice exits with an error if TLS is not available.

  9. Enter heuristics commands to assist in quorum calculation, or leave the field blank to skip this step.

    You can enter one command, multiple commands separated by semicolons, or the path to a script file. The commands can be written in any programming language.

    If you enter heuristics commands, you must also select the mode of operation. The default is sync.

    • sync: QDevice runs heuristics when the cluster services start (or restart), when the cluster membership changes, and when nodes connect to the QNetd server.

    • on: QDevice runs heuristics in the same scenarios as sync and also at regular intervals.

  10. If required, the script prompts you for the password of the QNetd server, then configures passwordless SSH authentication between the cluster nodes and the QNetd server.

    The script configures QDevice on the nodes and completes the QNetd server's configuration, including generating CA and server certificates and starting the corosync-qnetd service. The script also checks whether a cluster restart is required and whether it is safe to do so automatically. If any non-STONITH resources are running, the script warns you to restart the cluster services manually.

  11. If you need to restart the cluster services manually, follow these steps to avoid resource downtime:

    1. Put the cluster into maintenance mode:

      > sudo crm maintenance on

      In this state, the cluster stops monitoring all resources. This allows the services managed by the resources to keep running while the cluster restarts. However, be aware that the resources will not have cluster protection while in maintenance mode.

    2. Restart the cluster services on all nodes:

      > sudo crm cluster restart --all
    3. Check the status of the cluster:

      > sudo crm status

      The nodes will have the status UNCLEAN (offline), but will soon change to Online.

    4. When the nodes are back online, put the cluster back into normal operation:

      > sudo crm maintenance off

4 Checking the QDevice and QNetd setup

Use the crm corosync status command to check the cluster's quorum status and the status of QDevice and QNetd. You can run this command from any node in the cluster.

The following examples show a cluster with two nodes (alice and bob) and a QNetd server (charlie).

Example 1: Showing the cluster's quorum status
> sudo crm corosync status quorum
1 alice member
2 bob member

Quorum information
------------------
Date:             [...]
Quorum provider:  corosync_votequorum
Nodes:            2
Node ID:          2
Ring ID:          1.e
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 alice
         2          1    A,V,NMW bob (local)
         0          1            Qdevice

The Membership information section shows the following status codes:

A (alive) or NA (not alive)

Shows the connectivity status between QDevice and Corosync.

V (vote) or NV (non vote)

Shows if the node has a vote. V means that both nodes can communicate with each other. In a split-brain scenario, one node would be set to V and the other node would be set to NV.

MW (master wins) or NMW (not master wins)

Shows if the master_wins flag is set. By default, the flag is not set, so the status is NMW.

NR (not registered)

Shows that the cluster is not using a quorum device.

Example 2: Showing the status of QDevice
> sudo crm corosync status qdevice
1 alice member
2 bob member

Qdevice information
-------------------
Model:                  Net
Node ID:                1
HB interval:            10000ms
Sync HB interval:       30000ms
Configured node list:
    0   Node ID = 1
    1   Node ID = 2
Heuristics:             Disabled
Ring ID:                1.e
Membership node list:   1, 2
Quorate:                Yes
Quorum node list:
    0   Node ID = 2, State = member
    1   Node ID = 1, State = member
Expected votes:         3
Last poll call:         [...]

Qdevice-net information
----------------------
Cluster name:           hacluster
QNetd host:             charlie:5403
Connect timeout:        8000ms
HB interval:            8000ms
VQ vote timer interval: 5000ms
TLS:                    Supported
Algorithm:              Fifty-Fifty split
Tie-breaker:            Node with lowest node ID
KAP Tie-breaker:        Enabled
Poll timer running:     Yes (cast vote)
State:                  Connected
TLS active:             Yes (client certificate sent)
Connected since:        [...]
Echo reply received:    [...]
Example 3: Showing the status of QNetd
> sudo crm corosync status qnetd
1 alice member
2 bob member

Cluster "hacluster":
    Algorithm:          Fifty-Fifty split (KAP Tie-breaker)
    Tie-breaker:        Node with lowest node ID
    Node ID 1:
        Client address:         ::ffff:192.168.1.185:45676
        HB interval:            8000ms
        Configured node list:   1, 2
        Ring ID:                1.e
        Membership node list:   1, 2
        Heuristics:             Undefined (membership: Undefined, regular: Undefined)
        TLS active:             Yes (client certificate verified)
        Vote:                   ACK (ACK)
    Node ID 2:
        Client address:         ::ffff:192.168.1.168:55034
        HB interval:            8000ms
        Configured node list:   1, 2
        Ring ID:                1.e
        Membership node list:   1, 2
        Heuristics:             Undefined (membership: Undefined, regular: Undefined)
        TLS active:             Yes (client certificate verified)
        Vote:                   No change (ACK)

5 Changing the QDevice or QNetd configuration

Use this procedure to change the configuration of QDevice or QNetd (for example, to change the tie-breaker method from lowest to highest).

  1. Log in either as the root user or as a user with sudo privileges.

  2. Put the cluster into maintenance mode:

    > sudo crm maintenance on

    In this state, the cluster stops monitoring all resources. This allows the services managed by the resources to keep running even when you stop the cluster services.

  3. Stop the cluster services on all nodes:

    > sudo crm cluster stop --all
  4. Open the Corosync configuration file:

    > sudo crm corosync edit
  5. Change the required setting in the quorum section, then save and close the file.

  6. Copy the new configuration to all nodes:

    > sudo crm corosync push
  7. Start the cluster service on all nodes:

    > sudo crm cluster start --all
  8. Check the status of the cluster:

    > sudo crm status

    The nodes will have the status UNCLEAN (offline), but will soon change to Online.

  9. When the nodes are back online, put the cluster back into normal operation:

    > sudo crm maintenance off
  10. Verify that the change was successful:

    > sudo crm corosync status qnetd

HA glossary

active/active, active/passive

How resources run on the nodes. Active/passive means that resources only run on the active node, but can move to the passive node if the active node fails. Active/active means that all nodes are active at once, and resources can run on (and move to) any node in the cluster.

arbitrator

An arbitrator is a machine running outside the cluster to provide an additional instance for cluster calculations. For example, QNetd provides a vote to help QDevice participate in quorum decisions.

CIB (cluster information base)

An XML representation of the whole cluster configuration and status (cluster options, nodes, resources, constraints and the relationships to each other). The CIB manager (pacemaker-based) keeps the CIB synchronized across the cluster and handles requests to modify it.

clone

A clone is an identical copy of an existing node, used to make deploying multiple nodes simpler.

In the context of a cluster resource, a clone is a resource that can be active on multiple nodes. Any resource can be cloned if its resource agent supports it.

cluster

A high-availability cluster is a group of servers (physical or virtual) designed primarily to secure the highest possible availability of data, applications and services. Not to be confused with a high-performance cluster, which shares the application load to achieve faster results.

Cluster logical volume manager (Cluster LVM)

The term Cluster LVM indicates that LVM is being used in a cluster environment. This requires configuration adjustments to protect the LVM metadata on shared storage.

cluster partition

A cluster partition occurs when communication fails between one or more nodes and the rest of the cluster. The nodes are split into partitions but are still active. They can only communicate with nodes in the same partition and are unaware of the separated nodes. This is known as a split brain scenario.

cluster stack

The ensemble of software technologies and components that make up a cluster.

colocation constraint

A type of resource constraint that specifies which resources can or cannot run together on a node.

concurrency violation

A resource that should be running on only one node in the cluster is running on several nodes.

Corosync

Corosync provides reliable messaging, membership and quorum information about the cluster. This is handled by the Corosync Cluster Engine, a group communication system.

CRM (cluster resource manager)

The management entity responsible for coordinating all non-local interactions in a High Availability cluster. SUSE Linux Enterprise High Availability uses Pacemaker as the CRM. It interacts with several components: local executors on its own node and on the other nodes, non-local CRMs, administrative commands, the fencing functionality, and the membership layer.

crmsh (CRM Shell)

The command-line utility crmsh manages the cluster, nodes and resources.

Csync2

A synchronization tool for replicating configuration files across all nodes in the cluster.

DC (designated coordinator)

The pacemaker-controld daemon is the cluster controller, which coordinates all actions. This daemon has an instance on each cluster node, but only one instance is elected to act as the DC. The DC is elected when the cluster services start, or if the current DC fails or leaves the cluster. The DC decides whether a cluster-wide change must be performed, such as fencing a node or moving resources.

disaster

An unexpected interruption of critical infrastructure caused by nature, humans, hardware failure, or software bugs.

disaster recovery

The process by which a function is restored to the normal, steady state after a disaster.

Disaster Recovery Plan

A strategy to recover from a disaster with the minimum impact on IT infrastructure.

DLM (Distributed Lock Manager)

DLM coordinates accesses to shared resources in a cluster, for example, managing file locking in clustered file systems to increase performance and availability.

DRBD

DRBD® is a block device designed for building High Availability clusters. It replicates data on a primary device to secondary devices in a way that ensures all copies of the data remain identical.

existing cluster

The term existing cluster is used to refer to any cluster that consists of at least one node. An existing cluster has a basic Corosync configuration that defines the communication channels, but does not necessarily have resource configuration yet.

failover

Occurs when a resource or node fails on one machine and the affected resources move to another node.

failover domain

A named subset of cluster nodes that are eligible to run a resource if a node fails.

fencing

Prevents access to a shared resource by isolated or failing cluster members. There are two classes of fencing: resource-level fencing and node-level fencing. Resource-level fencing ensures exclusive access to a resource. Node-level fencing prevents a failed node from accessing shared resources and prevents resources from running on a node with an uncertain status. This is usually done by resetting or powering off the node.

GFS2

Global File System 2 (GFS2) is a shared disk file system for Linux computer clusters. GFS2 allows all nodes to have direct concurrent access to the same shared block storage. GFS2 has no disconnected operating mode, and no client or server roles. All nodes in a GFS2 cluster function as peers. GFS2 supports up to 32 cluster nodes. Using GFS2 in a cluster requires hardware to allow access to the shared storage, and a lock manager to control access to the storage.

group

Resource groups contain multiple resources that need to be located together, started sequentially and stopped in the reverse order.

Hawk (HA Web Konsole)

A user-friendly Web-based interface for monitoring and administering a High Availability cluster from Linux or non-Linux machines. Hawk can be accessed from any machine that can connect to the cluster nodes, using a graphical Web browser.

heuristics

QDevice supports using a set of commands (heuristics) that run locally on start-up of cluster services, cluster membership change, successful connection to the QNetd server, or optionally at regular times. The result is used in calculations to determine which partition should have quorum.

knet (kronosnet)

A network abstraction layer supporting redundancy, security, fault tolerance, and fast fail-over of network links. In SUSE Linux Enterprise High Availability 16, knet is the default transport protocol for the Corosync communication channels.

local cluster

A single cluster in one location (for example, all nodes are located in one data center). Network latency is minimal. Storage is typically accessed synchronously by all nodes.

local executor

The local executor is located between Pacemaker and the resources on each node. Through the pacemaker-execd daemon, Pacemaker can start, stop and monitor resources.

location

In the context of a whole cluster, location can refer to the physical location of nodes (for example, all nodes might be located in the same data center). In the context of a location constraint, location refers to the nodes on which a resource can or cannot run.

location constraint

A type of resource constraint that defines the nodes on which a resource can or cannot run.

meta attributes (resource options)

Parameters that tell the CRM (cluster resource manager) how to treat a specific resource. For example, you might define a resource's priority or target role.

metro cluster

A single cluster that can stretch over multiple buildings or data centers, with all sites connected by Fibre Channel. Network latency is usually low. Storage is frequently replicated using mirroring or synchronous replication.

network device bonding

Network device bonding combines two or more network interfaces into a single bonded device to increase bandwidth and/or provide redundancy. When using Corosync, the bonded device is not managed by the cluster software. Therefore, the bonded device must be configured on every cluster node that might need to access it.

node

Any server (physical or virtual) that is a member of a cluster.

order constraint

A type of resource constraint that defines the sequence of actions.

Pacemaker

Pacemaker is the CRM (cluster resource manager) in SUSE Linux Enterprise High Availability, or the brain that reacts to events occurring in the cluster. Events might be nodes that join or leave the cluster, failure of resources, or scheduled activities such as maintenance, for example. The pacemakerd daemon launches and monitors all other related daemons.

parameters (instance attributes)

Parameters determine which instance of a service the resource controls.

primitive

A primitive resource is the most basic type of cluster resource.

promotable clone

Promotable clones are a special type of clone resource that can be promoted. Active instances of these resources are divided into two states: promoted and unpromoted (also known as active and passive or primary and secondary).

QDevice

QDevice and QNetd participate in quorum decisions. The corosync-qdevice daemon runs on each cluster node and communicates with QNetd to provide a configurable number of votes, allowing a cluster to sustain more node failures than the standard quorum rules allow.

QNetd

QNetd is an arbitrator that runs outside the cluster. The corosync-qnetd daemon provides a vote to the corosync-qdevice daemon on each node to help it participate in quorum decisions.

quorum

A cluster partition is defined to have quorum (be quorate) if it has the majority of nodes (or votes). Quorum distinguishes exactly one partition. This is part of the algorithm to prevent several disconnected partitions or nodes (split brain) from proceeding and causing data and service corruption. Quorum is a prerequisite for fencing, which then ensures that quorum is unique.

RA (resource agent)

A script acting as a proxy to manage a resource (for example, to start, stop or monitor a resource). SUSE Linux Enterprise High Availability supports different kinds of resource agents.

ReaR (Relax and Recover)

An administrator tool set for creating disaster recovery images.

resource

Any type of service or application that is known to Pacemaker, for example, an IP address, a file system, or a database. The term resource is also used for DRBD, where it names a set of block devices that use a common connection for replication.

resource constraint

Resource constraints specify which cluster nodes resources can run on, what order resources load in, and what other resources a specific resource is dependent on.

See also colocation constraint, location constraint and order constraint.

resource set

As an alternative format for defining location, colocation or order constraints, you can use resource sets, where primitives are grouped together in one set. When creating a constraint, you can specify multiple resources for the constraint to apply to.

resource template

To help create many resources with similar configurations, you can define a resource template. After being defined, it can be referenced in primitives or in certain types of constraints. If a template is referenced in a primitive, the primitive inherits all operations, instance attributes (parameters), meta attributes and utilization attributes defined in the template.

SBD (STONITH Block Device)

SBD provides a node fencing mechanism through the exchange of messages via shared block storage. Alternatively, it can be used in diskless mode. In either case, it needs a hardware or software watchdog on each node to ensure that misbehaving nodes are really stopped.

scheduler

The scheduler is implemented as pacemaker-schedulerd. When a cluster transition is needed, pacemaker-schedulerd calculates the expected next state of the cluster and determines what actions need to be scheduled to achieve the next state.

split brain

A scenario in which the cluster nodes are divided into two or more groups that do not know about each other (either through a software or hardware failure). STONITH prevents a split-brain scenario from badly affecting the entire cluster. Also known as a partitioned cluster scenario.

The term split brain is also used in DRBD but means that the nodes contain different data.

SPOF (single point of failure)

Any component of a cluster that, if it fails, triggers the failure of the entire cluster.

STONITH

An acronym for shoot the other node in the head. It refers to the fencing mechanism that shuts down a misbehaving node to prevent it from causing trouble in a cluster. In a Pacemaker cluster, STONITH is managed by the fencing subsystem pacemaker-fenced.

switchover

The planned moving of resources to other nodes in a cluster. See also failover.

utilization

Tells the CRM what capacity a certain resource requires from a node.

watchdog

SBD (STONITH Block Device) needs a watchdog on each node to ensure that misbehaving nodes are really stopped. SBD feeds the watchdog by regularly writing a service pulse to it. If SBD stops feeding the watchdog, the hardware enforces a system restart. This protects against failures of the SBD process itself, such as becoming stuck on an I/O error.