Report group CHANNEL

The utilization of channels cannot be directly determined. In section “Performance of an 8-Gbit channel” you will find standard values for the throughputs that can be achieved in practice. It is recommended that only around 60% of these throughputs are exploited:

• Very high channel throughputs do not necessarily show high performance, but can indicate a bottleneck. The highest channel throughputs are normally achieved with a large number of tasks, each of which can only achieve a low proportion of the total throughput.

• By contrast, a small number of tasks that are not influenced and thus operating at high performance do not generally exploit the maximum possible channel throughput.

• Excessively high channel loads may therefore indicate that too many devices are attached to the same channel. However, the use of page chaining also makes the channel load too high. For this reason this function should only be used if it brings about distinct advantages. This is always the case if all the blocks transferred in one I/O operation are required and there is no need for further I/O operations.

When comparing channel throughputs, always take into account the fact that FC channels achieve their specified throughput in each transmission direction. Higher throughputs are thus possible for mixed reading and writing than for pure reading or writing.

Channel throughput with VM2000 operation:

Recording of the input/output rate is guest system specific. Therefore, the throughputs output relate to a guest system.

Channel throughput for x86 servers

The information in the description of the CHANNEL-IO monitoring program in the “openSM2 (BS2000) [18 (Related publications)]” manual must be taken into account.