Chapter 7. Sysplex functions 169
Draft Document for Review April 7, 2004 6:15 pm 6947ch07.fm
Figure 7-7 System-managed CF structure duplexing
Whenever possible, try to comply with the following recommendations:
򐂰Provide two or more physical CF-to-CF links (peer mode), or two or more physical
CF-to-CF links in each direction (sender/receiver mode), between each pair of CFs
participating in duplexing. The physical CF-to-CF links may be shared by a combination of
z/OS-to-CF links and CF-to-CF links.
򐂰For redundancy, provide two or more z/OS-to-CF links from each system to each CF.
Provide dedicated z/OS-to-CF links if possible. If z/OS-to-CF links are shared between
z/OS partitions, the occurrence of path busy conditions should be limited to at most 10 to
20 percent of total requests. If path busy exceeds this guideline, either provide dedicated
links, or provide additional shared links, to eliminate or reduce the contention for these link
resources. Use peer links whenever possible.
򐂰You can provide either dedicated or shared z/OS CPs when using system-managed CF
structure duplexing. Dedicated Coupling Facility CPs are highly recommended for
system-managed CF structure duplexing.
򐂰Be prepared to provide additional z/OS CPU capacity when the workload’s CF operations
become duplexed. Provide sufficient Coupling Facility CP resources so that Coupling
Facility CP utilization remains below 50% in all CF images.
򐂰Provide “balanced” Coupling Facility CP capacity between duplexed pairs of CFs. Avoid
significant imbalances such as one CF with shared CPs and the other CF with dedicated
CPs, CFs with wildly disparate numbers of CPs, CFs of different machine types with very
different raw processor speed, and so forth.
򐂰As z/OS-to-CF and CF-to-CF distances increase, monitor the Coupling Facility link
subchannel and path-busy status. If more than 10% of all messages are being delayed on
the CF link due to subchannel or path busy conditions, either migrate to peer mode links to
increase the number of subchannels for each link, or configure an additional link.
򐂰In a GDPS/PPRC multi-site configuration, do not duplex CF structure data between
coupling facilities located in different sites; rather, if desired, duplex the structures between
two coupling facilities located at the same site. CF structure data is not preserved in GDPS
site failover situations, regardless of duplexing.
A technical paper on system-managed CF structure duplexing is available at:
http://www-1.ibm.com/servers/eserver/zseries/library/techpapers/gm130103.html

z/OS ICF

z800/z900/z990/z890/G5/G6 z800/z900/z990/z890/G5/G6

z/OS

ICF

CF to CF link
connectivity required
for System-managed
CF structure duplexing