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:
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. |