When you are installing and configuring OMEGAMON XE For Storage there are quite a few options in the ICAT installation panels. Most of these options are fairly straight forward (such as sampling intervals for tape, cache control units, etc.). But, as I've mentioned in earlier posts, the most critical options revolve around the specification of the DASD collection options.
There are several options that control DASD collection, and there are some subtleties to the optimal way to specify collection. In the example shown here, Option 2 is where you can specify DASD collection frequency, and Option 3 is where you can specify devices to exclude from monitoring. If you can exclude some devices from ongoing monitoring, it may be a good idea to do so, and save the cost of monitoring.
Option 2 (DASD Device Monitoring) is the most critical panel to review. When you set up collection options here, you can either collect information every nth I/O (sample count) or collect when the device exceeds a specified MSR (millisecond response time) threshold. The example screen shot I show, has the default configuration panel. What you get by default is every I/O will be monitored, so my first recommendation is to not just automatically take the default. Take the time to configure the options on this panel.
First you can create an entry that will specify a VOLSER or device range. Once you have specified your devices, you then have a choice of monitoring I/O based on sampling (every n I/Os) or monitoring the device if a specified MSR threshold is exceeded. In the Monitor Status field, if you specify ON, then you will monitior based on the number specified in the Sample cnt/MSR field. But, if you enter MSR in the Monitoring Status option, I/O monitoring will happen if the device exceeds the MSR threshold. The Sample cnt/MSR field is treated as an MSR level setting, and the other part of the magic is that the MSR/exception trip count specified in the top portion of the panel comes into play.
Perhaps a little confusing, but obviously these options make a big difference in terms of how much data is gathered on an ongoing basis. If you want to keep the cost of collection down, then consider using the MSR option to collect when exceptions occur. If you want more data on an ongoing basis, then consider the sample approach, but set the sample frequency higher than the defualt of 1 (which means collect everything).