Intel 170 Servers, AS/400 RISC Server, 7xx Servers manual Sizing when using Micro-Partitioning

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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