On 1/16/2013 3:37 AM, Paul Fenstermacher wrote:
Ending the system "controlled" flushes the disk cache from memory to disk,
> "immediate" does not do this.

Nope, not a fact.

The disk IOAs need time to write the contents to disk. Ending controlled allows for the IOA to do its normal thing and put data onto disk just as it would if the system were running.

For most IPLs, it really doesn't make any difference because you're likely bringing the system right back up. It is when you are shutting down and not planning to bring the system back up for days or weeks when it will be important to make sure the contents of cache get written out. Maybe Ias a precautionary measure due to an impending natural disaster like a hurricane?

Another time when you want to make sure the cache is written is if you will be relocating the IOAs and disk behind them to another system. My advice to make sure it happens is to end controlled, IPL to DST, shutdown, IPL to DST again, and finally shut down. I don't remember the specifics now, but the multiple IPLs to DST do something to make sure every bit gets written to disk.

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