An Introduction to IMS: Your Complete Guide to IBMs Information Management System

XRF works by having a second, alternate, IMS running. The alternate IMS runs on a separate z/OS image that, preferably, is on a physically separate machine that is channel-attached to the first one. The alternate IMS tracks the work of the active IMS system by reading the IMS log data sets of the active IMS system. XRF provides the ability to perform hardware maintenance and maintenance on other system software products without interrupting the availability of the IMS application.

The principal drawbacks of XRF are:

• XRF does not protect against application errors. If the outage is caused by an application error, the same application message might be re-presented on the alternate IMS and cause it to fail.

• XRF does not protect against network outages. You must plan for this separately.

• XRF does not support DB2 databases.

• Occasionally, you must apply IMS maintenance to both the active and standby IMS systems at the same time.

Although XRF can prevent most unplanned and planned outages, it cannot keep the IMS system available indefinitely. You must eventually plan outages for software maintenance, upgrades, and some changes to the IMS configuration. IMS systems running with XRF have achieved continuous availability for years.