The iSeries 400 usually does a good job of spreading data across all drives on the system, but occasionally you can have situations where a disk drive or two appear to be doing most of the work. That's usually due to adding new disk drives to an existing configuration. You could also have a situation where you have older and newer drives of different speeds.
It would be nice to have data that's accessed most often on your faster drives. The iSeries does a better job of balancing and managing disk usage than probably any other machine in the industry, but there are times when things get a little out of sync. As of V4R4, IBM has provided a solution that will address several disk performance issues. It is the STRASPBAL command.
The STRASPBAL has the option of balancing disk utilization in one of three ways, and IBM defines the options in this way:
Capacity Balancing -- The data on all the units within the ASP will be balanced so each unit has an equal percentage of used and unused space.
Usage Balancing -- The high-use and low-use data on each unit in the ASP is redistributed to balance the arm utilization of each unit within the specified ASP.
Hierarchical Storage Management Balancing -- The high-use and low-use data on each unit in the ASP is redistributed so that the high-use data resides on high performance units and the low-use data resides on low performance units.
If you're using capacity balancing, you can run the STRASPBAL command without having to gather any usage information, although I would recommend running this command during a time when there's little system activity. If you're going to use the Usage Balancing or the Hierarchical Storage Management Balancing, you first need to run the TRCASPBAL to gather the proper information for this command to use.
One other interesting feature about these commands is their consideration for the user. If you have short periods of time in which you want to run the commands, the STRASPBAL and the TRCASPBAL allow you to specify a time frame for the commands to run. In the case of the STRASPBAL command, the next time the command is started, it will pick up where it left off. That will allow you to spread your balancing over several days.
Completion messages are sent to QHST, so the following command is handy if you want to see only information pertaining to these commands. DSPLOG MSGID(CPI1474 CPI1475 CPI1476 CPI1477 CPI1478).
I use the STRASPBAL command every time I add new disk drives, and in my opinion this is one command that was long overdue.
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About the author: Tim is vice president of Technical Services at Interlink Technologies in Maumee, Ohio, where he serves as chief architect for their warehouse management system. He has worked in the banking, insurance, healthcare and distribution industries in various positions, including programmer/analyst, systems analyst and DP manager. Tim has worked on IBM midrange platforms since 1983.
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