DB2 UDB provides high availability failover support on many platforms.
On AIX, DB2 UDB supports failover through the capabilities of IBM High
Availability Cluster Multi-Processing (HACMP). Failover capability
allows for the automatic transfer of workload from one processor to another
should there be a hardware failure.
HACMP provides increased availability through clusters of processors which
share resources such as disks or network access. If one processor fails
then another in the cluster can substitute for the failed one.
|Note:||Do not use a "kill -9" against the db2start process in a high
availability environment. This action is not recommended in any
environment, but in particular such an action may invalidate failover recovery
in your high availability environment.
There are three modes of failover support provided, a brief description of
each mode and its application to DB2 follows. In each case we use the
simple scenario of a two processor HACMP cluster.
- Hot Standby
- One processor is being actively used to run your DB2 instance and the
second 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
- Both processors are either used to run separate DB2 instances, or one is
use to run a DB2 instance while the other 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 failing
processor. Once the failover is complete, the remaining processor is
doing the work of both processors.
- Concurrent Access
- Multiple processors can be used to scale to a single database instance
using the DB2 Universal Database Extended Enterprise Edition product.
This is done using a shared-nothing model and 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, then
the other processor will take over the partitions of the failing
processor. DB2 UDB Extended Enterprise Edition does not require the use
of a Concurrent Resource Manager to provide redundancy. DB2 co-exists
with the Concurrent Resource Manager, but does not require its
capability. Redundancy is managed by using the previous two
modes. The capabilities of this mode are only required by database
managers with a shared architecture.
Each of the above 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.
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