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Draft Document for Review April 7, 2004 6:15 pm

Cost benefits are realized by enabling the use of non-standalone Coupling Facilities (for example, ICFs) for all resource sharing and data sharing environments.

7.3.2 CF Structure Duplexing

System-managed Coupling Facility structure duplexing creates a duplexed copy of the structure in advance of any failure, providing a robust failure recovery capability through failover to the unaffected structure instance. This results in:

￿An easily-exploited common framework for duplexing the structure data contained in any type of CF structure, with installation control over which structures are duplexed

￿Minimized overhead of duplexing during mainline operation via hardware-assisted serialization and synchronization between the primary and secondary structure updates

￿Maximized availability in failure scenarios by providing a rapid failover to the unaffected structure instance of the duplexed pair, with very little disruption to the ongoing execution of work by the exploiter and applications

System-managed duplexing rebuild provides robust failure recovery capability via the redundancy of duplexing, and low exploitation cost via system-managed, internalized processing. Structure failures, CF failures, or losses of CF connectivity can be handled by:

1.Hiding the observed failure condition from the active connectors to the structure, so that they do not perform unnecessary recovery actions

2.Switching over to the structure instance that did not experience the failure

3.Re-establishing a new duplex copy of the structure if appropriate as the Coupling Facility becomes available again, or on a third CF in the Parallel Sysplex

System messages are generated as the structure falls back to simplex mode for monitoring and automation purposes. The structure operates in simplex mode until a new duplexed structure can be established, and can be recovered using whatever existing recovery techniques are supported by the exploiter.

System-managed duplexing's main focus is providing thisrobust recovery capability for structures whose users do not support user-managed duplexing rebuild processes, or do not even support user-managed rebuild at all.

7.3.3 Configuration planning

A new connectivity requirement for system-managed CF structure duplexing is that there must be bi-directional CF-to-CF connectivity between each pair of CFs in which duplexed structure instances reside. With peer links, this connectivity can be provided by a single bi-directional link (two with redundancy).

CF-to-CF links can either be dedicated or shared via MIF. They can be shared with z/OS-to-CF links between z/OS and Coupling Facility images in the pair of servers they connect. When planning sharing links, remember that receiver links cannot be shared, and peer links can only be shared by one Coupling Facility partition.

168IBM eServer zSeries 990 Technical Guide

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IBM 990 manual CF Structure Duplexing, Configuration planning

990 specifications

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