IBM 990 7.5.5 Special considerations and restrictions

6947ch07.fm Draft Document for Review April 7, 2004 6:15 pm

182 IBM eServer zSeries 990 Technical Guide

Within an LPAR cluster, the prioritization is managed by WLM goal mode and coordinated

across the cluster. Hence the range should be set identically for all logical partitions in the

same LPAR cluster.

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 Table7-5 on page 182.

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 7-5 WLM CSS priority range mapping with specified range less than 8

7.5.5 Special considerations and restrictions

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-u nique naming creates problems in terms

of scope of control.

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.

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 FF FF FF FF FF FF FF

Importance 1&2 missing goals FE FE FE FE FE FE FF

Importance 3&4 missing goals FD FE FE FE FE FE FF

Meeting goals. Adjust by ratio of

connect time to elapsed time. FC-F9 FD-FA FD-FB FD-FC FD FE FF

Discretionary F8 F9 FA FB FC FD FE