Sizing When Using Micro-Partitioning - IBM 170 Servers Manual

14.6.3.2 Sizing when using Micro-Partitioning

Defining Virtual SCSI servers in micro-partitions enables much better granularity of processor
resource sizing and potential recovery of unused processor time by uncapped partitions.
Tempering those benefits, use of micro-partitions for Virtual SCSI servers slightly increases I/O
response time and creates somewhat more complex processor entitlement sizing.
The sizing methodology should be based on the same operation costs as for IBM i operating
system Server partitions. However, additional entitlement should be added for running in
micro-partitions. We recommend that the IBM i operating system Server partition be configured
as uncapped so it can take advantage of unused capacity of other partitions, it is possible to get
more processor time to service I/O.
Because I/O latency with Virtual SCSI varies with the machine utilization and IBM i operating
system Server topology, consider the following:
1. For the most demanding I/O traffic (high bandwidth or very low latency), try to use native
I/O.
2. If using Virtual I/O and the system contains enough processors, consider putting the IBM i
operating system Server in a dedicated processor partition.
3. If using a Micro-Partitioning IBM i operating system Server, use as few virtual processors as
possible.
4. In order to avoid latency issues try to always size the CPU generously
IBM i 6.1 Performance Capabilities Reference - January/April/October 2008
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Copyright IBM Corp. 2008 Chapter 14 DASD Performance 240