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.