Stopping i5 UPS Usage Before Something Ugly Happens

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:

• Writes all current job data to main storage (disk)
• Ends all currently running jobs and subsystems
• Powers down the system

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:

• *BASIC or *CALC. IBM’s V5R3 explanation for QUPSDLYTIM states that these two values perform the same function on all OS/400 V3R6 and above operating systems, as well as on all i5/OS V5 systems. When set to *BASIC or *CALC, the system will perform a controlled shutdown after 200 seconds.
• A set amount of time between 0 and 99999 seconds. You can set QUPSDLYTIM to a value that is more compatible with your actual UPS capacity. If you have a small UPS that is intended just for brownout situations or if the UPS batteries are undercharged or old, you can set QUPSDLYTIM to a value below 200 seconds. If you have a more robust UPS system, you can set the value higher than 200 seconds, although I doubt many people have a UPS system that can keep a system running for as long as 99999 seconds (1.157 days). A value of zero (0) indicates that there is no QUPSDLYTIM value in effect and a controlled system shutdown will start immediately after the UPS kicks in.
• *NOMAX. The system will not power down on its own. It will remain running until either the power comes back on or it crashes abnormally because the UPS power was drained. If using this value, you must also set a valid message queue name in the Uninterruptible power supply message queue system value (QUPSMSGQ). The QUPSMSGQ value must specify a workstation message queue name, the QSYSOPR message queue, or another message queue. Any workstation message queue specified in QUPSMSGQ (or QSYSOPR) must already be allocated to an interactive job that is running in break or notify mode. A specified non-workstation message queue merely has to be allocated to a job. If QUPSMSGQ is not set to a proper value when QUPSDLYTIM is set to *NOMAX and a power outage occurs, the system will begin an immediate power down. So watch out for this configuration trick.

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.

–Joe

RELATED SOURCES

IBM, Uninterruptible power supply delay time system value Web page, iSeries Information Center, Version 5 Release 3

IT Jungle Forums, Automatic Shutdown