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Understanding Clustering

Windowsclustering comes in different levels of availability or options. Determine which fault-tolerant option is best.

Active/Active Clustering —In Active/Active clustering, all servers in the cluster are live andservicing clients at the same time. Active/Active clustering is limited to two clusterednodes.

Active/Passive Clustering —In Active/Passive clustering, clustering is available when two ormore nodes are available. Only one server in the cluster can service end users at atime. Active/Passive clusters are also limited to a per-application basis while theother server(s) wait in a standby or offline mode until a failure occurs. If a failure occurs, the passive node then begins to service clients. In this configuration, onevirtual server is configured and shared by both nodes.

Heartbeat—A single User Datagram Protocol (UDP) packet is sent every 500milliseconds between nodes in the cluster across the internal private network thatrelays health information of the cluster nodes and on the health of the clusteredapplication. If there is no response during a heartbeat, the cluster begins a failover.

Failover—Failover is the process of one node in the cluster changing states fromoffline to online, resulting in the node taking over responsibility.

Failback—Failback is the process of moving virtual server applicationsthat failed over in the cluster back to the original online node.

Quorum resource—This is the shared disk that holds the cluster server’s configurationinformation. All servers must be able to contact the quorum resource to become part of anServer Cluster.

Resource group—A resource group is a collection of cluster resources, such as the Server NetBIOS name, TCP/IP address, and services of the Cluster. Aresource  group also defines which items fail over to the surviving nodes duringfailover. This also includes cluster resource items, including cluster disk. A resourcegroup is owned by only one node in the cluster at a time.

Cluster resource—Cluster resources are vital information of the virtualserver and include its network TCP/IP addresses, NetBIOS name, disks, andservices

Majority node cluster—In this configuration, each node is responsible forcontributing one local disk to the quorum disk set that is used as storage disks. Thisconfiguration limits the majority-of-node-resource to one owner at a time. Thisconfiguration requires a minimum of two nodes to be available at all times.

Quorum-device cluster—Using the quorum type resource requires the clusterstorage resource to be connected with a Fibre Channel or small computer systeminterface (SCSI) bus. In this configuration, any physical disk can be configured as aquorum disk.

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