For each structure discussion that follows, there is an indication of the
approximate percentage that is eligible for non-control storage residency. Refer
to Appendix B, “RMF Reporting in Parallel Sysplex” on page 187 for sample
RMF (Postprocessor) reports that report on CF usage and can assist in the
tuning of the CF storage. Also, the D CF command displays total storage
allocation for the CF, broken into control and non-control storage.
2.2.3 Structure Placement
Structure placement is essentially the process of satisfying the demands of the
CF users with the resources available. There are a few absolutes:
The sum of the structure space must be less than the storage available on a
CF.
Do not configure any CF so that a single CF failure can cause a catastrophic
outage. It is far better to run degraded than not to run at all. Make certain
that there is sufficient white space and processing capacity in the remaining
CFs to allow the exploiters to rebuild their structures somewhere else and
continue operation.
Define the preference list for each structure in the CFRM policies in such a
way as to allow it to be rebuilt into another CF. That is, each structure's
preference list should contain multiple CFs. This is also true for those
structures that do not support rebuild. Define multiple CFs in the preference
list in case one of the CFs is not available at initial allocation time.
Multiple CFRM policies may be needed with preference list variations to
enable certain structures to be moved to accommodate CF service activities.
A structure
cannot
be split across CFs. A structure exists in one and only
one CF at any point in time. Multiple structures may exist for the same
exploiter, for example XCF, but each structure is unique by name.
There are some architectural and implementation limitations:
A CF can only contain 63 structures at CF level 0 and 1. A CF can
contain up to 1023 structures at CF level 2 or above.
The CFRM policy supports 255 structure definitions. This is increased to
512 with APAR OW19974.
CF list and lock structures support 32 connectors.
CF cache structures support 64 connectors at CF level 2 and above.
APAR OW15447 provides support for up to 255 connectors to cache
structures at CF level 2.
Note:
The number of structures and connectors to structures is constrained
by whatever is defined on the ITEM NAME(STR) and ITEM NAME(CONNECT)
statements in the CFRM policy.
Few installations will go from an uncoupled environment to a coupled
environment, with all application data being fully shared among all applications,
in one step. More likely, it will involve a staged approach. For example,
perhaps the users of the CF will be in this order: XCF first, then OS/390 Security
Server (RACF), then JES2, then OS/390 Communications Server (VTAM), and so
on, until many exploiting functions have structures. After experience has been
gained, applications and their databases will be migrated. Perhaps even
additional CPCs and additional CFs will be added to the Parallel Sysplex before
the migration is completed.
Chapter 2. A Structured View of CF Structures
77

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