Stopping i5 UPS Usage Before Something Ugly Happens
March 8, 2006 Hey, Joe
We recently installed an i5 520 machine. We also experienced a power failure that lasted longer than our UPS could sustain, and the system wound up ending abnormally. Do you know how to set up an i5/OS system so that it automatically shuts down its partitions during a power failure? I have searched the IBM knowledgebase in vain.
— From the IT Jungle Forums
Yes, IBM provides a way to do this with the Uninterruptible Power Supply Delay Time system value (QUPSDLYTIM). According to IBM, this value is available for several different versions of the OS/400 and i5/OS operating system, starting with OS/400 V3R6 all the way up through i5/OS V5. Here’s how it works.
QUPSDLYTIM is the system timer that i5/OS uses to determine how long to wait after a power outage occurs before it does the following things:
Once a power outage occurs and the timer value specified in QUPSDLYTIM is exceeded, i5/OS will perform these functions and power down the system for its own protection. QUPSDLYTIM works with your uninterruptible power supply (UPS) to do two things.
First, it allows you to set a timer value that should be sufficient for the UPS to continue to power the system in the event of a short power outage. If your UPS can potentially power your server for 15 minutes, you may want to set QUPSDLYTIM to some shorter value–say, 600 seconds (10 minutes)–so your system can continue processing during a brown-out or short-duration outage. QUPSDLYTIM allows you to avoid unnecessary system shut-downs due to minor power problems.
In the event of a longer outage, where the UPS cannot power the system through the problem, QUPSDLYTIM sounds the alarm to shut down the system as cleanly as possible. It does this by saving production data that has not yet been written to permanent storage and, to minimize file corruption, by ending jobs and subsystems in an emergency system shutdown process. QUPSDLYTIM protects your system from unnecessary data corruption.
QUPSDLYTIM can be set to one of the following values:
The shipped value for QUPSDLYTIM is *CALC.
When setting QUPSDLYTIM to a numeric value, there are, again, two issues to think about.
The first concerns your expected UPS battery life. QUPSDLYTIM must always be set lower than expected battery life because the system will take extra time to write main storage information to disk. It also takes some time to close system jobs and perform the actual power down. IBM provides some tips and tables for calculating the time needed for these tasks on its QUPSDLYTIM Web page, but some experts recommend setting QUPSDLYTIM to a value that is anywhere between 50 to 80 percent of your battery uptime to complete these tasks before the UPS gives out. The trick here is that it’s not an exact science to predict the time needed for a controlled system shutdown, and you should err on the side of caution when setting your QUPSDLYTIM value.
The final issue concerns the batteries in the UPS themselves. Over time, even fully charged batteries may not retain 100 percent of their original capacity. Batteries will degrade, and IBM states that a typical battery will lose 20 to 50 percent of its rated capacity over five years. So you will also need to factor battery condition into your QUPSDLYTIM number.
Hope this helps.
IBM, Uninterruptible power supply delay time system value Web page, iSeries Information Center, Version 5 Release 3
IT Jungle Forums, Automatic Shutdown