Cluster Server 7.4.1 Administrator's Guide - Linux
- Section I. Clustering concepts and terminology
- Introducing Cluster Server
- About Cluster Server
- About cluster control guidelines
- About the physical components of VCS
- Logical components of VCS
- Types of service groups
- About resource monitoring
- Agent classifications
- About cluster control, communications, and membership
- About security services
- Components for administering VCS
- About cluster topologies
- VCS configuration concepts
- Introducing Cluster Server
- Section II. Administration - Putting VCS to work
- About the VCS user privilege model
- Administering the cluster from the command line
- About administering VCS from the command line
- About installing a VCS license
- Administering LLT
- Starting VCS
- Stopping the VCS engine and related processes
- Logging on to VCS
- About managing VCS configuration files
- About managing VCS users from the command line
- About querying VCS
- About administering service groups
- Modifying service group attributes
- About administering resources
- Enabling and disabling IMF for agents by using script
- Linking and unlinking resources
- About administering resource types
- About administering clusters
- Configuring applications and resources in VCS
- VCS bundled agents for UNIX
- Configuring NFS service groups
- About NFS
- Configuring NFS service groups
- Sample configurations
- About configuring the RemoteGroup agent
- About configuring Samba service groups
- About testing resource failover by using HA fire drills
- Predicting VCS behavior using VCS Simulator
- Section III. VCS communication and operations
- About communications, membership, and data protection in the cluster
- About cluster communications
- About cluster membership
- About membership arbitration
- About membership arbitration components
- About server-based I/O fencing
- About majority-based fencing
- About the CP server service group
- About secure communication between the VCS cluster and CP server
- About data protection
- Examples of VCS operation with I/O fencing
- About cluster membership and data protection without I/O fencing
- Examples of VCS operation without I/O fencing
- Administering I/O fencing
- About the vxfentsthdw utility
- Testing the coordinator disk group using the -c option of vxfentsthdw
- About the vxfenadm utility
- About the vxfenclearpre utility
- About the vxfenswap utility
- About administering the coordination point server
- About configuring a CP server to support IPv6 or dual stack
- About migrating between disk-based and server-based fencing configurations
- Migrating between fencing configurations using response files
- Controlling VCS behavior
- VCS behavior on resource faults
- About controlling VCS behavior at the service group level
- About AdaptiveHA
- Customized behavior diagrams
- About preventing concurrency violation
- VCS behavior for resources that support the intentional offline functionality
- VCS behavior when a service group is restarted
- About controlling VCS behavior at the resource level
- VCS behavior on loss of storage connectivity
- Service group workload management
- Sample configurations depicting workload management
- The role of service group dependencies
- About communications, membership, and data protection in the cluster
- Section IV. Administration - Beyond the basics
- VCS event notification
- VCS event triggers
- Using event triggers
- List of event triggers
- Virtual Business Services
- Section V. Veritas High Availability Configuration wizard
- Introducing the Veritas High Availability Configuration wizard
- Administering application monitoring from the Veritas High Availability view
- Administering application monitoring from the Veritas High Availability view
- Administering application monitoring from the Veritas High Availability view
- Section VI. Cluster configurations for disaster recovery
- Connecting clusters–Creating global clusters
- VCS global clusters: The building blocks
- About global cluster management
- About serialization - The Authority attribute
- Prerequisites for global clusters
- Setting up a global cluster
- About IPv6 support with global clusters
- About cluster faults
- About setting up a disaster recovery fire drill
- Test scenario for a multi-tiered environment
- Administering global clusters from the command line
- About global querying in a global cluster setup
- Administering clusters in global cluster setup
- Setting up replicated data clusters
- Setting up campus clusters
- Connecting clusters–Creating global clusters
- Section VII. Troubleshooting and performance
- VCS performance considerations
- How cluster components affect performance
- How cluster operations affect performance
- VCS performance consideration when a system panics
- About scheduling class and priority configuration
- VCS agent statistics
- About VCS tunable parameters
- Troubleshooting and recovery for VCS
- VCS message logging
- Gathering VCS information for support analysis
- Troubleshooting the VCS engine
- Troubleshooting Low Latency Transport (LLT)
- Troubleshooting Group Membership Services/Atomic Broadcast (GAB)
- Troubleshooting VCS startup
- Troubleshooting issues with systemd unit service files
- Troubleshooting service groups
- Troubleshooting resources
- Troubleshooting sites
- Troubleshooting I/O fencing
- Fencing startup reports preexisting split-brain
- Troubleshooting CP server
- Troubleshooting server-based fencing on the VCS cluster nodes
- Issues during online migration of coordination points
- Troubleshooting notification
- Troubleshooting and recovery for global clusters
- Troubleshooting licensing
- Licensing error messages
- Troubleshooting secure configurations
- Troubleshooting wizard-based configuration issues
- Troubleshooting issues with the Veritas High Availability view
- VCS message logging
- VCS performance considerations
- Section VIII. Appendixes
How preferred fencing works
The I/O fencing driver uses coordination points to prevent split-brain in a VCS cluster. At the time of a network partition, the fencing driver in each subcluster races for the coordination points. The subcluster that grabs the majority of coordination points survives whereas the fencing driver causes a system panic on nodes from all other subclusters. By default, the fencing driver favors the subcluster with maximum number of nodes during the race for coordination points.
This default racing preference does not take into account the application groups that are online on any nodes or the system capacity in any subcluster. For example, consider a two-node cluster where you configured an application on one node and the other node is a standby-node. If there is a network partition and the standby-node wins the race, the node where the application runs panics and VCS has to bring the application online on the standby-node. This behavior causes disruption and takes time for the application to fail over to the surviving node and then to start up again.
The preferred fencing feature lets you specify how the fencing driver must determine the surviving subcluster. The preferred fencing solution makes use of a fencing parameter called node weight. VCS calculates the node weight based on online applications, system capacity, and site preference details that you provide using specific VCS attributes, and passes to the fencing driver to influence the result of race for coordination points. At the time of a race, the racer node adds up the weights for all nodes in the local subcluster and in the leaving subcluster. If the leaving subcluster has a higher sum (of node weights) then the racer for this subcluster delays the race for the coordination points. Thus, the subcluster that has critical systems or critical applications wins the race.
The preferred fencing feature uses the cluster-level attribute PreferredFencingPolicy that takes the following race policy values:
Disabled (default): Preferred fencing is disabled.
When the PreferredFencingPolicy attribute value is set as Disabled, VCS sets the count based race policy and resets the value of node weight as 0.
System: Based on the capacity of the systems in a subcluster.
If one system is more powerful than others in terms of architecture, number of CPUs, or memory, this system is given preference in the fencing race.
When the PreferredFencingPolicy attribute value is set as System, VCS calculates node weight based on the system-level attribute FencingWeight.
See ???.
Group: Based on the higher priority applications in a subcluster.
The fencing driver takes into account the service groups that are online on the nodes in any subcluster.
In the event of a network partition, I/O fencing determines whether the VCS engine is running on all the nodes that participate in the race for coordination points. If VCS engine is running on all the nodes, the node with higher priority service groups is given preference during the fencing race.
However, if the VCS engine instance on a node with higher priority service groups is killed for some reason, I/O fencing resets the preferred fencing node weight for that node to zero. I/O fencing does not prefer that node for membership arbitration. Instead, I/O fencing prefers a node that has an instance of VCS engine running on it even if the node has lesser priority service groups.
Without synchronization between VCS engine and I/O fencing, a node with high priority service groups but without VCS engine running on it may win the race. Such a situation means that the service groups on the loser node cannot failover to the surviving node.
When the PreferredFencingPolicy attribute value is set as Group, VCS calculates node weight based on the group-level attribute Priority for those service groups that are active.
Site: Based on the priority assigned to sites in a subcluster.
The Site policy is available only if you set the cluster attribute SiteAware to 1. VCS sets higher weights to the nodes in a higher priority site and lesser weights to the nodes in a lower priority site. The site with highest cumulative node weight becomes the preferred site. In a network partition between sites, VCS prefers the subcluster with nodes from the preferred site in the race for coordination points.
See Site attributes.