Introduction To The Power7 Hypervisor - IBM Power7 Optimization And Tuning Manual

3.1 Introduction to the POWER7 Hypervisor

Power Virtualization was introduced in POWER5 systems, so there are many reference
materials that are available that cover all three resources (CPU, memory, and I/O),
virtualization, capacity planning, and virtualization management. Some of these documents
are shown in the reference section at the end of this section, which focuses on POWER7
Virtualization usually. As for any workload deployments, capacity planning, selecting the
correct set of technologies, and appropriate tuning are critical to deploying high performing
workloads. However, in deploying workloads in virtualized environments, there are more
aspects to consider, such as consolidation ratio, workload resource usage patterns, and the
suitability of a workload to run in a shared resource environment (or latency requirements).
The first step in the virtualization deployment process is to understand if the performance of a
workload in a shared resource environment meets customer requirements. If the workload
requires consistent performance with stringent latency requirements, then such workloads
must be deployed on a dedicated partition rather than on a shared LPAR. The exceptions are
where shared processor pool is not heavily over committed and overutilized; such workloads
could meet stringent requirements in a shared LPAR configuration also.
It is a preferred practice to understand the resource usage of all workloads that are planned
for consolidation on a single system, especially when you plan to use a shared resource
model, such as shared LPARs, IBM Active Memory™ Sharing, and VIO server technologies.
The next step is to use a capacity planning tool that takes virtualization impacts into
consideration, such as the IBM Workload Estimator, to estimate capacity for each partition.
One of the goals of virtualization is maximizing usage. This usage can be achieved by
consolidating workloads that peak at different times (that is, in a non-overlapping manner, so
each workload (or partition) does not have to be sized for peak usage but rather for average
usage). At the same time, each workload can grow to consume free resources from the
shared pool that belong to other partitions on the system. This situation allows the packing of
more partitions (workloads) on a single system, producing a higher consolidation ratio or
higher density on the deployed system. A higher consolidation ratio is a key metric to achieve
in the data center, as it helps to reduce the total cost of ownership (TCO).
Let us look at a list of key attributes that require consideration when deploying workloads on a
shared resource model (virtualization):
Levels of variation between average and peak usage of workloads:
– A large difference between average and peak usage
– A small difference between average and peak usage
Workloads and their peak duration, frequency, and estimate when they potentially peak:
Select workloads that peak at different times (non-over lapping).
Workload Service Level Agreement SLA requirements (latency requirements and their
tolerance levels).
Ratio of active to inactive (mostly idle) partitions on a system.
Provisioning and de-provisioning frequency.
IBM PowerVM has a richer set of technology options than virtualization on other platforms.
It supports dedicated, shared, and a mix of dedicated and shared resource models for
each of the system resources, such as processor cores, memory, and I/O:
– Shared LPAR: Capped versus uncapped.
– Shared LPAR: Resources overcommit levels to meet the peak usage (the ratio of
virtual processors to physical processor entitled capacity).
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POWER7 and POWER7+ Optimization and Tuning Guide