Administration Guide

Chapter 11. Designing for High Availability

DB2 Universal Database provides high availability failover support on many platforms. Failover capability allows for the automatic transfer of workload from one processor to another when there is hardware failure. For example, on AIX, DB2 UDB supports failover through the capabilities of IBM High Availability Cluster Multi-Processing (HACMP). Throughout this section, examples from AIX are used to introduce the concepts associated with high availability.

HACMP provides increased availability through clusters of processors that share resources such as disks or network access. If a processor fails, another processor in the cluster substitutes for it.

There are three modes of failover support:

Hot Standby

In this mode, one processor is used to run your DB2 instance, and the second processor is in standby mode, ready to take over the instance if there is an operating system or hardware failure involving the first processor.

Mutual Takeover

In this mode:

• Both processors are used to run separate DB2 instances.
• One processor is used to run a DB2 instance, while the other one is used to run DB2 applications.

If there is an operating system or hardware failure on one of the processors, the other processor takes over the tasks of the failed processor, eventually doing the work of both processors.

Concurrent Access

In this mode, multiple processors are used to scale to a single database instance using the DB2 Universal Database Enterprise - Extended Edition (EEE) product. This is done using a shared-nothing model, partitioning the data such that one or more partitions are running on each processor in the cluster. If an operating system or hardware failure occurs on one of the processors, the other processor takes over the partitions of the failing processor. DB2 UDB EEE does not require a Concurrent Resource Manager to provide redundancy. Redundancy is managed by using the hot standby or the mutual takeover mode. The capabilities of the concurrent access mode are only required by database managers with a shared architecture.

Each of these configurations can be used to failover one or more partitions of a partitioned database. In addition, each can failover a complete instance of a single partition installation.