Executive Summary
The DB2 High Availability Disaster Recovery (HADR) feature is a database replication method that provides a high-availability solution for both partial and complete site failures. HADR protects against data loss by replicating data changes from a source database, called the primary, to one or more target databases, called the standbys.
The multiple standby HADR feature provides database administrators (DBAs) with a single technology to provide both high availability (HA) as well as disaster recovery (DR). This paper shows how HADR multiple standbys can be set up, configured, and monitored. In addition, various examples demonstrate how HADR multiple standbys behave in different failure scenarios.
Introduction
You can use DB2 High Availability and Disaster Recovery (HADR) to create a warm copy of a database on a separate site by using the database transaction log shipping method. Beginning in DB2 Version 10.1, the feature is enhanced to support up to three standby databases. Having multiple standbys enables the combination of high availability (HA) and disaster recovery (DR) scenarios for a single database multisite data replication. Additionally, when a multiple standby setup is coupled with the other HADR enhancements for Version 10.1, log spooling, and delayed replay, it allows quick recovery from a user error or an errant transaction. To enable HADR multiple-standby mode, use the new hadr_target_list database configuration parameter. The number of entries specified by this parameter on the primary determines the number of standbys a primary database has. Details about multiple standby configurations follow in subsequent sections.
Traditional HADR features and functionalities work with multiple standbys as well. For example, reads on standby are supported on any standby. Any standby can perform forced or graceful takeover operations. There are important considerations including recovery point objective and automatic reconfiguration regarding the takeover operation for multiple standbys. Details follow later. Furthermore, cluster manager automation using IBM Tivoli System Automation for Multiplatforms (SA MP) is supported for multiple standby configurations with a primary database and one of the standby databases. Rolling upgrade is also supported by the multiple standby feature.
You can easily convert a single standby configuration to a multiple standby configuration. Details on conversion are presented in the
Setting up a multiple standby system section.
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