IBM eServer zSeries 900 Technical Guide

Chapter 2. zSeries 900 system structure 25

A standard SAP configuration provides a very well balanced system for most environments.

However, there are application environments with very high I/O rates (typically some TPF

environments), and in this case additional SAPs can increase the capability of the channel

subsystem to perform I/O operations. Additional SAPs can be added to a configuration by

either ordering optional SAPs or assigning some CPs as SAPs. Orderable SAPs may be

preferred since they do not incur software charges, as when CPs are assigned as SAPs.

In the z900 servers the number of SAPs can be greater than the number of CPs and the

number of used STIs. Changing the number of SAPs is

disruptive

to a z900 configuration.

Optional additional orderable SAPs

An available option on some general purpose models is additional orderable SAPs. These

additional SAPs increase the capacity of the channel subsystem to perform I/O operations

without impacting the number of PUs assigned as CPs. Optional orderable SAPs can vary

from 0 for models with no extra PUs to from 1 to 5, depending on the model. All configurations

must have at least one spare PU (see Table 2-3 on page 36 and Table 2-4 on page 37).

Note that z900 Models 109, 116 and 216 have no additional orderable SAP capability.

Optionally assignable SAPs

Depending on the model of the general purpose models, up to five available general purpose

CPs may be optionally assigned as SAPs instead of CPs. This reassignment capability better

balances the resources of the general purpose models for some TPF environments.

No additional action is necessary if you intend to activate a modified server configuration in a

basic operating mode. However, if you intend to activate a modified server configuration with

a modified SAP configuration in logically partitioned (LPAR) mode, a reduction in the number

of CPs available will reduce the number of logical processors you can activate. Activation of a

logical partition will fail if the number of logical processors you attempt to activate exceeds the

number of CPs available. To avoid a logical partition activation failure, you should verify that

the number of logical processors assigned to a logical partition does not exceed the number

of CPs available.

2.2.4 Reserved Processors

In LPAR mode, Reserved Processors can be defined to a logical partition. Reserved

Processors are implemented by the Processor Resource/System Manager (PR/SM) to allow

nondisruptive

image upgrades. Reserved processors are like “spare logical processors.”

They can be defined as Shared or Dedicated to CPs, IFLs, or ICFs.

Reserved processors can be dynamically configured online by an operating system that

supports this function, if there are enough physical processors available to satisfy this

request. The previous PR/SM rules regarding logical processor activation remain unchanged.

Reserved Processors also provide the capability of defining to a logical partition more logical

processors than the number of available physical processors in a configuration. This makes it

possible to configure nondisruptively online more logical processors after additional physical

processors have been made available concurrently, via CUoD, CIU or CBU.

Without the Reserved Processors definition, a logical partition processor upgrade is

disruptive, requiring:

a. The partition deactivation.

b. A Logical Processor definition change.

c. The partition activation.