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Monitoring and Planning Link Effectiveness

z/OS environments

FICON Channels

When analyzing FICON channels, it is normally not possible to draw conclusions based on their utilization alone: 60% may or may not be a good value; it really depends on the type of work being done. With FICON being a multiplexing technology, a measure that is more indicative of how well the FICON channel is dealing with individual I/O requests is the effective channel rate, i.e. how much time does the channel need to transfer a given amount of data. A low effective data rate indicates that there is much demand for the channel, which causes connect time elongation and thereby increases I/O service time. IntelliMagic Vision computes and charts FICON Effective Channel Data Rate, as in the chart below.

 

 

In this example the installation might be concerned about the effective data rate of their DS8000 (“DS8-2” represented by the yellow line) dropping to about half of its peak value during a critical part of their online window. Note that the chart is an interesting illustration of technological progress over three generations of disk subsystems and their FICON capabilities!

Open Exchanges

Another way to evaluate FICON performance is by monitoring the number of open exchanges: i.e. how many I/Os are being served at the same time by the FICON channel. A high number, as is the case for the two ESS F20 machines in the chart below, indicates that the channel is dealing with more I/O requests than it can handle without delays. Note that the maximum number for an ESS F20 is 32. Taking into consideration that the chart represents 15 minute intervals, both ESS F20 subsystems must experience periods where they are running into the 32 open exchange limit.

 

 

FICON and ISL

IntelliMagic Vision can be used for the sizing and monitoring of FICON configurations, including those with inter-switch links (ISL). With IntelliMagic Vision you can determine the throughput on any channel, ESCON or FICON, and you can easily determine how much bandwidth is needed for each disk subsystem.  Once directors are installed, you can report FICON director statistics including those on the ISL links with IntelliMagic Vision.  Planning ISLs can be difficult, because you need to know the load from each system for your disk subsystems. IntelliMagic Vision provides this information for a particular point in time or for an extended period.

 

You can find a complete description of the FICON sizing process in our paper 'Sizing your ESCON to FICON Conversion', by Gilbert Houtekamer and Steve Guendert.

 

Distributed and z/OS Storage Systems

HA Utilization

Often times the aggregate throughput of a storage system's host adapter is less than the sum of the individual parts.  Unfortunately most tools do not report the cumulative throughput or I/O rates for an entire host adapter.  IntelliMagic automatically computes the sum of the key metrics for all ports on a given host adapter to provide an easy means to interpret the utilization of the host adapters.