Partition Availability Priority - IBM BladeCenter PS700 Technical Overview And Introduction

The POWER7 family of systems continues to offer and introduce significant enhancements
that can increase system availability, and to drive towards a high availability objective with
hardware components that can perform the following functions:
Self-diagnose and self-correct during run time
Automatically reconfigure to mitigate potential problems from suspect hardware
Self-heal or to substitute good components for failing components automatically
Note: POWER7 processor-based servers are independent of the operating system for
error detection and fault isolation within the central electronics complex.
Throughout this chapter, we describe IBM POWER technology's capabilities that are focused
on keeping a system environment up and running. For a specific set of functions that are
focused on detecting errors before they become serious enough to stop computing work, see
4.4.1, "Detecting" on page 110.

4.3.1 Partition availability priority

Also available is the ability to assign availability priorities to partitions. If an alternate
processor recovery event requires spare processor resources and there are no other means
of obtaining the spare resources, the system determines which partition has the lowest
priority and attempts to claim the needed resource. On a properly configured POWER
processor-based server, this approach allows that capacity to be first obtained from a low
priority partition instead of a high priority partition.
This capability is relevant to the total system availability because it gives the system an
additional stage before an unplanned outage. In the event that insufficient resources exist to
maintain full system availability, these servers attempt to maintain partition availability by
user-defined priority.
Partition-availability priority is assigned to partitions by using a weight value or integer rating.
The lowest priority partition is rated at 0 (zero) and the highest priority partition is valued at
255. The default value is set at 127 for standard partitions and 192 for Virtual I/O Server
(VIOS) partitions. You can vary the priority of individual partitions.
Note: Integrated Virtualization Manager (IVM) must be installed in partition number one on
the PS700, PS701, and PS702 blades when installing multiple LPARs. On IVM-managed
blades, the priority value for the LPARs is changed by using the chsycfg command with the
lpar_avail_priority flag.
Partition-availability priorities can be set for both dedicated and shared processor partitions.
The POWER Hypervisor uses the relative partition weight value among active partitions to
favor higher priority partitions for processor sharing, adding and removing processor capacity,
and favoring higher priority partitions for normal operation.
The partition specifications for minimum, desired, and maximum capacity are taken into
account for capacity-on-demand options, and if total system-wide processor capacity
becomes disabled because of deconfigured failed processor cores. For example, if total
system-wide processor capacity is sufficient to run all partitions with the minimum capacity,
the partitions are allowed to start or continue running. If processor capacity is insufficient to
run a partition at its minimum value, starting that partition results in an error condition that
must be resolved.
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IBM BladeCenter PS700, PS701, and PS702 Technical Overview and Introduction