5 special considerations and restrictions – IBM 990 User Manual

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IBM

zSeries 990 Technical Guide

WLM sets priorities within a range of eight values that will be mapped to the specified range.
If a larger range is specified, WLM uses the top eight values. If a smaller range is specified,
WLM maps its values into the smaller range, retaining as much function as possible within the
allowed range. Note that the WLM calculated priority is still a range of 8. The mapped priority
is shown in Table 7-6.

A range of eight values is recommended for CSS I/O priority-capable logical partitions. If the
logical partition is run in compatibility mode or with I/O priority management disabled, the I/O
priority is set to the middle of the specified range.

Table 7-6 WLM CSS priority range mapping with specified range less than 8

7.5.5 Special considerations and restrictions

Here we discuss some special considerations and restrictions of Sysplex functions.

Unique LPAR cluster names

LPAR clusters, running on a 2064, 2066, 2084, or 2086 server, must be uniquely named. This
is the sysplex name that is associated with the LPAR cluster. Managed channels have an
affinity (are owned by) a specific LPAR cluster. Non-unique naming creates problems in terms
of scope of control.

Disabling Dynamic Channel Path Management

To disable Dynamic Channel Path Management within an LPAR cluster running z/OS, turning
off the function by using the SETIOS DCM=OFF command is not sufficient. Although a
necessary step, this does not ensure that the existing configuration is adequate to handle
your workload needs, since it leaves the configuration in the state it was at the time the
function was disabled. During your migration to DCM, we would recommend that you
continue to maintain your old IODF until you are comfortable with DCM. This will allow you to
back out of DCM by activating a known configuration.

Automatic I/O interface reset

When going through all of the steps to enable Dynamic Channel Path Management, also
ensure that the “Automatic input/output (I/O) interface reset” option is enabled on the
Hardware Management Console. This will allow Dynamic Channel Path Management to
continue functioning in the event that one participating system image fails.

This is done by enabling the option in the reset profile used to activate the server. Using the
“Customize/Delete Activation Profiles task” available from the “Operational Customization
tasks list,” open the appropriate reset profile and then open the Options page to enable the
option.

WLM CSS priorities
(range width)

Calculated
range (8)

Specified
range (7)

(6)

(5)

(4)

(3)

(2)

System work.

Importance of 1 and 2 missing
goals.

Importance of 3 and 4 missing
goals.

Meeting goals. Adjust by ratio of
connect time to elapsed time.

FC-F9

FD-FA

FD-FB

FD-FC

Discretionary.