Glossary

Agent

A process that starts, stops, and monitors all configured resources of a type, and reports their status to VCS.

Active/Active Configuration

A failover configuration where each systems runs a service group. If either fails, the other one takes over and runs both service groups. Also known as a symmetric configuration.

Active/Passive Configuration

A failover configuration consisting of one service group on a primary system, and one dedicated backup system. Also known as an asymmetric configuration.

Authentication Broker

The VERITAS Security Services component that serves, one level beneath the root broker, as an intermediate registration authority and a certification authority. The authentication broker can authenticate clients, such as users or services, and grant them a certificate that will become part of the VERITAS credential. An authentication broker cannot, however, authenticate other brokers. That task must be performed by the root broker. See Root Broker.

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Cluster

One or more computers linked together for the purpose of multiprocessing and high availability. The term is used synonymously with VCS cluster, meaning one or more computers that are part of the same GAB membership.

Disaster Recovery

A solution that supports fail over to a cluster in a remote location in the event that the local cluster becomes unavailable. Disaster recovery global clustering, heartbeating, and replication.

Disk Heartbeats (GABDISK)

A heartbeat placed on a physical disk shared by all systems in the cluster.

Failover

A failover occurs when a service group faults and is migrated to another system.

GAB

Group Atomic Broadcast (GAB) is a communication mechanism of the VCS engine that manages cluster membership, monitors heartbeat communication, and distributes information throughout the cluster.

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Global Service Group

A VCS service group that spans across two or more clusters. The ClusterList attribute for the group contains the list of clusters over which the group spans.

hashadow Process

A process that monitors and, when required, restarts HAD.

High Availability Daemon (HAD)

The core VCS process that runs on each system. The HAD process maintains and communicates information about the resources running on the local system and receives information about resources running on other systems in the cluster.

Jeopardy

A node is in jeopardy when it is missing one of the two required heartbeat connections. When a node is running with one heartbeat only (in jeopardy), VCS does not restart the applications on a new node. This action of disabling failover is a safety mechanism that prevents data corruption.

LLT

Low Latency Transport (LLT) is a communication mechanism of the VCS engine that provides kernel-to-kernel communications and monitors network communications.

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main.cf

The file in which the cluster configuration is stored.

Network Partition

If all network connections between any two groups of systems fail simultaneously, a network partition occurs. When this happens, systems on both sides of the partition can restart applications from the other side resulting in duplicate services, or "split-brain." A split brain occurs when two independent systems configured in a cluster assume they have exclusive access to a given resource (usually a file system or volume). The most serious problem caused by a network partition is that it affects the data on shared disks. See Jeopardy and Seeding.

Node

The physical host or system on which applications and service groups reside. When systems are linked by VCS, they becomes nodes in a cluster.

N-to-1

An N-to-1 configuration is based on the concept that multiple, simultaneous server failures are unlikely; therefore, a single backup server can protect multiple active servers. When a server fails, its applications move to the backup server. For example, in a 4-to-1 configuration, one server can protect four servers, which reduces redundancy cost at the server level from 100 percent to 25 percent.

N-to-N

N-to-N refers to multiple service groups running on multiple servers, with each service group capable of being failed over to different servers in the cluster. For example, consider a four-node cluster with each node supporting three critical database instances. If any node fails, each instance is started on a different node, ensuring no single node becomes overloaded.

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N-to-M

N-to-M (or Any-to-Any) refers to multiple service groups running on multiple servers, with each service group capable of being failed over to different servers in the same cluster, and also to different servers in a linked cluster. For example, consider a four-node cluster with each node supporting three critical database instances and a linked two-node back-up cluster. If all nodes in the four-node cluster fail, each instance is started on a node in the linked back-up cluster.

Replication

Replication is the synchronization of data between systems where shared storage is not feasible. The systems that are copied may be in local backup clusters or remote failover sites. The major advantage of replication, when compared to traditional backup methods, is that current data is continuously available.

Resources

Individual components that work together to provide application services to the public network. A resource may be a physical component such as a disk or network interface card, a software component such as Oracle8i or a Web server, or a configuration component such as an IP address or mounted file system.

Resource Dependency

A dependency between resources is indicated by the keyword "requires" between two resource names. This indicates the second resource (the child) must be online before the first resource (the parent) can be brought online. Conversely, the parent must be offline before the child can be taken offline. Also, faults of the children are propagated to the parent.

Resource Types

Each resource in a cluster is identified by a unique name and classified according to its type. VCS includes a set of predefined resource types for storage, networking, and application services.

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Root Broker

The first authentication broker, which has a self-signed certificate. The root broker has a single private domain that holds only the names of brokers that shall be considered valid. See Authentication Broker.

Seeding

Seeding is used to protect a cluster from a pre-existing network partition. By default, when a system comes up, it is not seeded. Systems can be seeded automatically or manually. Only systems that have been seeded can run VCS. Systems are seeded automatically only when: an unseeded system communicates with a seeded system or all systems in the cluster are unseeded and able to communicate with each other. See Network Partition.

Service Group

A service group is a collection of resources working together to provide application services to clients. It typically includes multiple resources, hardware- and software-based, working together to provide a single service.

Service Group Dependency

A mechanism by which two service groups can be linked by a dependency rule.

Shared Storage

Storage devices that are connected to and used by two or more systems.

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SNMP Notification

Simple Network Management Protocol (SNMP) developed to manage nodes on an IP network.

State

The current activity status of a resource, group or system.

types.cf

The types.cf file describes standard resource types to the VCS engine; specifically, the data required to control a specific resource.

Virtual IP Address

A unique IP address that associated with the cluster. It may be brought up on any system in the cluster, along with the other resources of the service group. This address, also known as the IP alias should not be confused with the base IP address, which is the IP address that corresponds to the host name of a system.