Does An IPL Really Help Improve System Performance?

Published: March 17, 2010

Hey, Joe:

My i/OS system performance hasn't been very good lately and my storage usage is starting to shoot up. I'm thinking I should IPL my System i 550 box to reset the system. Will an IPL help me regain storage and improve performance?

--Tom

The short answer is. . . it depends. Being IT professionals who also deal with Windows machines, sometimes our first response to bad system performance is to reboot the system. Fortunately for iSeries, System i, and Power i administrators, we don't IPL our systems as much as others may reboot their Windows boxes, and we can usually terminate or restart runaway applications without restarting the entire system.

However, just as some Windows administrators best advice is to "reboot it" when there's a problem with a Windows system, it's also common practice in the iSeries, System i, and Power i world that an i/OS IPL "can do a system good when it's ailing."

According to common knowledge, an IPL generally does three things that can help improve system performance.

1. Clears out temporary storage
2. Reinitializes the system
3. Reloads system and program objects

While all this is true, I have not been able to find any definitive IBM documents that discuss how an IPL improves system performance or retrieves used disk space, other than to clear out all possible offending jobs and start over again from scratch. I also called IBM and asked them for material on the benefits of an IPL and they weren't able to produce anything.

It's even difficult to find a definitive listing of all the steps that i/OS executes during an IPL. Online information is big on how to IPL and how to perform special functions during an IPL; it's not so big on how an IPL improves system performance and disk usage. (Note: if anyone reading this can provide definitive documentation on this subject, please feel free to forward it to me and I may use your information in a future article.)

Without proper documentation as to what an IPL does and how it benefits storage and performance issues, my feeling is that no one can say for sure that an IPL will restore disk space or improve performance. An IPL may solve your problems if they are fixable by clearing out temporary storage or reinitializing the system, but you may have been able to take care of things on your own without kicking everyone off the system.

Not that I'm saying that you shouldn't ever use an IPL to improve system performance or reduce storage. I would instead recommend that an IPL should only be taken as a last step to correct system problems when everything else has failed. I recommend that you look at other alternatives to solving these issues, and there are a number of articles on detecting and curing i/OS system and storage problems, including:

• An article I wrote called Another Way to Retrieve i5 System Storage Space, which shows how to use the Retrieve Disk Information and Print Disk information commands to examine where your disk space is being used and to locate system storage hogs. You might also want to check out this article on hunting down storage hogs.
• To determine how much temporary storage space is being used on your system, review this article to find out which jobs are using excessive temporary storage and how to retrieve that space.
• There are many articles out there for troubleshooting system performance issues. And because i/OS jobs and entire subsystems can be ended and restarted without affecting other jobs and subsystems, if you can identify which jobs are causing your problem (which can usually be accomplished by looking for the jobs with the highest CPU utilization) you have the option to only reinitialize the offending job, not the entire system.

While an IPL does have its place in reinitializing your system and solving problems, it shouldn't be treated as the best or only way to take care of system issues. I'd encourage anyone to think larger about their system issues, rather than performing a knee-jerk reaction and attempting to IPL their box whenever a short-term performance problem occurs. Instead, I recommend a thorough investigation of your issue and an attempt to understand and fix the problem, knowing you have a last ditch option to reset the system if nothing else works.

HTH

--Joe

RELATED STORIES

Hunting Down Storage Hogs

How Much Temporary Storage Am I Using?

Another Way to Retrieve i5 System Storage Space

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