Intel 170 Servers, AS/400 RISC Server, 7xx Servers manual

yThe new server algorithm only applies to the new hardware available in V4R5 (2xx, 8xx and SBx models). The behavior of all other hardware, such as the 7xx models is unchanged (see section 2.2.3 Existing Model section for 7xx algorithm).

2.2.2 Choosing Between Similarly Rated Systems

Sometimes it is necessary to choose between two systems that have similar CPW values but different processor megahertz (MHz) values or L2 cache sizes. If your applications tend to be compute intensive such as Java, WebSphere, EJBs, and Domino, you may want to go with the faster MHz processors because you will generally get faster response times. However, if your response times are already sub-second, it is not likely that you will notice the response time improvements. If your applications tend to be L2 cache friendly such as many traditional commercial applications are, you may want to choose the system that has the larger L2 cache. In either case, you can use the IBM eServer Workload Estimator to help you select the correct system (see URL: http://www.ibm.com/iseries/support/estimator ) .

2.2.3 Existing Older Models

Server model behavior applies to:

yAS/400 Advanced Servers

yAS/400e servers

yAS/400e custom servers

yAS/400e model 150

yiSeries model 170

yiSeries model 7xx

Relative performance measurements are derived from commercial processing workload (CPW) on iSeries and AS/400. CPW is representative of commercial applications, particularly those that do significant database processing in conjunction with journaling and commitment control.

Traditional (non-server) AS/400 system models had a single CPW value which represented the maximum workload that can be applied to that model. This CPW value was applicable to either an interactive workload, a client/server workload, or a combination of the two.

Now there are two CPW values. The larger value represents the maximum workload the model could support if the workload were entirely client/server (i.e. no interactive components). This CPW value is for the processor feature of the system. The smaller CPW value represents the maximum workload the model could support if the workload were entirely interactive. For 7xx models this is the CPW value for the interactive feature of the system.

The two CPW values are NOT additive - interactive processing will reduce the system's client/server processing capability. When 100% of client/server CPW is being used, there is no CPU available for interactive workloads. When 100% of interactive capacity is being used, there is no CPU available for client/server workloads.

For model 170s announced in 9/98 and all subsequent systems, the published interactive CPW represents the point (the "knee of the curve") where the interactive utilization may cause increased overhead on the system. (As will be discussed later, this threshold point (or knee) is at a different value for previously announced server models). Up to the knee the server/batch capacity is equal to the processor capacity (CPW) minus the interactive workload. As interactive requirements grow beyond the knee, overhead

IBM i 6.1 Performance Capabilities Reference - January/April/October 2008
© Copyright IBM Corp. 2008	Chapter 2 - Server Performance Behavior	18