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HP-UX System Administrator's Guide: Routine Management Tasks: HP-UX 11i Version 3 > Appendix A Using High Availability Strategies
Using Serviceguard |
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An Serviceguard cluster is a networked grouping of HP 9000 servers (nodes) having sufficient redundancy of software and hardware that a single point of failure will not significantly disrupt service. Applications and services are grouped together in packages. In the event of a service, node, or network failure, Serviceguard can automatically transfer control of all system resources in a designated package to another node within the cluster, allowing the applications to remain available with minimal system interruption. Serviceguard replaces the earlier SwitchOver product which also allowed for redundant computer systems. Serviceguard first became available with HP-UX 10.0. To provide a high level of availability, a typical cluster uses redundant system components, for example, two or more processing cores and two or more independent disks. This redundancy eliminates any single point of failure. In general, the more redundancy, the greater access you will have to applications, data, and supportive services in the event of failure. In addition to hardware redundancy, the system must have the software support that enables and controls the transfer of applications to another server or network after a failure. Serviceguard provides the following support:
The primary disadvantages for Serviceguard are the additional cost of software and hardware redundancy and the added complexity of administration. Also, hardware failures on shared components may adversely affect all systems that are jointly connected. Serviceguard is an excellent choice for high availability data protection. It may be used in conjunction with other high availability products. HP ReferencesUsing a feature called automatic rotating standby, you can configure a cluster that lets you use one node as a substitute in the event a failure occurs. Any package would fail over to the node containing the fewest running packages. HP ReferenceTo reduce the amount of time needed for HP-UX operating system upgrades as well as application upgrades and patches, you can provide what is called a rolling upgrade. For a system with many components, the typical scenario is to bring down the entire cluster, upgrade every node to the new version of the software, and then restart the application on all the affected nodes. For large systems, this could result in a long downtime. An alternative is to provide for a rolling upgrade. A rolling upgrade rolls out the new software in a phased approach by upgrading only one component at a time without bringing down your clusters. This process can also be used any time one system needs to be taken offline for hardware maintenance. HP ReferenceYou can use shared tape devices in an Serviceguard cluster allowing high availability backups using tape libraries and tools such as Omniback. The ATS facility allows a two-node to four-node cluster to share standalone magnetic tape devices and/or tape library robotic devices. As a result, even after a package fails on one node, a backup of the package data continues or restarts on an alternate node. Device files corresponding to each tape or library robotic mechanism are created and written to an ATS ASCII configuration file. ATS uses this file to keep track of the devices configured in the cluster. HP Reference |
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