HP-UX System Administrator's Guide: Routine Management Tasks

A Using High Availability Strategies
High availability is the term used to describe computer systems that have been
configured so as to minimize the percentage of time that they will be down or otherwise
unavailable, and as a result, allow for the greatest degree of usefulness. High system
availability is achieved by minimizing the possibility that a hardware failure or a
software defect will result in a loss of the use of the system or in a loss of its data.
Improved system and data availability can therefore result from advantageous use of
either hardware and/or software components which serve to reduce the impact of errors
by making use of redundant and isolated components such as dual busses, I/O devices,
and duplicate copies of data.
Some of the various means of implementing high availability that should be considered
in administering HP-UX systems are reviewed here.
NOTE: High availability is a complex topic that can only be briefly summarized here.
For a more complete technical discussion, please refer to the white paper, Choosing the
Right Disk Technology in a High Availability Environment. This document can be found
on the HP documentation web site, http://docs.hp.com. Select “High Availability”
and then “White Papers.”
HP References
• HP-UX System Administrator’s Guide: Logical Volume Management
• Configuring OPS Clusters with ServiceGuard OPS Edition
• Managing Serviceguard
• Designing Disaster Tolerant High Availability Clusters
• HP-UX ServiceControl User’s Guide
• Using Advanced Tape Services
• Using High Availability Monitors
• Clusters for High Availability: A Primer of HP Solutions, HP Press, published by
Prentice Hall PTR, 1996
• Disk and File Management Tasks on HP-UX, HP Press, published by Prentice Hall
PTR, 1997
Using Software Mirroring as a Disk Protection Strategy
Data redundancy is necessary to prevent instances in which a single disk failure can
cause a system to go down until the problem is located and corrected. There are two
methods of providing data redundancy: software mirroring and hardware mirroring.
Each represents RAID Level 1. (See “Using Disk Arrays” (page 206) for more information
on the meaning of the various RAID levels.)
Software mirroring allows you to maintain identical copies of your data (except for
the root disk), so that each set of data has, in effect, a perfect clone of itself. In the event
a disk fails, the system can use the mirrored copy of the data, thus allowing users to
Using Software Mirroring as a Disk Protection Strategy 205