Chapter 2. System structure and design 51
Draft Document for Review April 7, 2004 6:15 pm 6947ch02.fm

Optionally assignable SAPs

Assigned CPs may be optionally reassigned as SAPs instead of CPs, using the Reset Profile
on the Hardware Management Console (HMC). This reassignment increases the capacity of
the Channel Subsystem to perform I/O operations, usually for some specific workloads or I/O
intensive testing environments.
if you intend to activate a modified server configuration with a modified SAP configuration, 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.
Reserved processors
Reserved processors can be defined to a logical partition. Reserved processors are defined
by the Processor Resource/System Manager (PR/SM) to allow non-disruptive capacity
upgrade. Reserved processors are like “spare logical processors.” They can be defined as
Shared or Dedicated.
Reserved processors can be dynamically configured online by an operating system that
supports this function if there are enough unassigned PUs 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 CPs, IFLs, ICFs, and zAAPs in the configuration.
This makes it possible to configure online, non-disruptively, more logical processors after
additional CPs, IFLs, ICFs, and zAAPs have been made available concurrently, via CUoD,
CIU, and On/Off CoD for CPs, IFLs, ICFs, and zAAPs, or CBU for CPs. See “Concurrent
upgrades” on page 186 for more details.
When no reserved processors are defined to a logical partition, a processor upgrade in that
logical partition is disruptive, requiring the following tasks:
1. Partition deactivation
2. A Logical Processor definition change
3. Partition activation
The maximum number of Reserved processors that can be defined to a logical partition
depends upon the number of logical processors that are defined. For an ESA/390 mode
logical partition the sum of defined and reserved logical processors is limited to 32, including
CPs and zAAPs. However up to 24 processors, including CPs and zAAPs, are planned to be
supported by z/OS 1.6. The z/VM 5.1 is planned to support up to 24 processors, either all
CPs or all IFLs.
For more information about logical processors and reserved processors definition, see
“Logical Partitioning overview” on page57.
Processor unit characterization
Processor unit (PU) characterization is done at Power-on Reset time when the server is
initialized. The z990 is always initialized in LPAR mode, and it is the PR/SM hypervisor that
has responsibility for the PU assignment.
Note: Concurrent upgrades are not supported with CPs defined as additional SAPs.