FICON Express2 Channel Performance Version 1.0 - IBM

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FICON Express2 Channel Performance Version 1.0 Page 9 response time components for 4K bytes/io, 3:1 r/w ratio, 70 to 80% cu cache hit ratio FICON Processor utilization 10% FPU 20% FPU 30% FPU 40% FPU 50% FPU 60% FPU 70% FPU 0 1 2 3 4 5 response times in ms Figure 7 pend disc conn Figures 8 and 9 represent two different ways of looking at the results of the 6x27k read hit benchmark. Figure 8 is a plot of response times and FICON processor utilization for the 6x27K read hit benchmark. Since this workload transfers over 165,000 bytes per I/O using a block size of 27K bytes, it stresses the links and buses more than it does the FICON channel processor. The maximum I/Os per second achieved was only 1100 io/sec which only drove the FICON processor utilization to about 40%. Therefore the channel processor is really not the resource that prevents this workload from achieving higher throughput. In general, for workloads that use large block sizes such as the 27K byte half-track size, it makes more sense to look at MB/sec instead of I/O per second and bus or link utilizations instead of processor utilizations. Figure 9 shows that this workload achieves 200 MB/sec which is the limit of the 2 Gbps link.
FICON Express2 Channel Performance Version 1.0 Page 10 z990 FEx2 6x27K Read hits response times & FPU vs io/sec avg response time in ms 5 100 90 4 80 70 3 60 50 2 40 30 1 20 10 0 0 0 200 400 600 800 1000 1200 1400 io/sec per channel Figure 8 In Figure 9, we look at the results of this same 6x27K read hit benchmark measurement with response times and FICON link utilization vs. MB/sec. FICON channel link utilizations are not directly reported on RMF but can be easily calculated by dividing the READ or WRITE MB/sec by the link capacity. In this case, with 2 Gpbs links, the capacity is approximately 200MB/sec. Here we see that the 2 Gbps link is the limit to achieving higher throughput since it is the resource that is being pushed closest to 100% utilization. The “knee of the response time” curve generally occurs between 70 and 80% link utilizations. If you are more interested in throughput than response times, then these utilization levels may be acceptable. If, however, you are running response time sensitive workloads then it might be more appropriate to keep link utilizations below 50%. FICON processor util% FEx2 resp time FEx2 FPU
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FICON Express2 Channel Performance Version 1.0 - IBM

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