RE: Cache battery and Raid Controller Design WAS: Re: Rép. : Question of a Newbie to POWER Systems

Yes. There's enough of a delay in the shutdown that the cache gets written
to disk.

Paul Nelson
Office 512-392-2577
Cell 708-670-6978
nelsonp@xxxxxxxxxxxxx


-----Original Message-----
From: midrange-l-bounces@xxxxxxxxxxxx
[mailto:midrange-l-bounces@xxxxxxxxxxxx] On Behalf Of Chuck Lewis
Sent: Wednesday, March 30, 2011 1:31 PM
To: Midrange Systems Technical Discussion
Subject: RE: Cache battery and Raid Controller Design WAS: Re: Rép. :
Question of a Newbie to POWER Systems

If you have a UPS and suffer a power outage would just powering the system
down force the cache to disk?

-----Original Message-----
From: midrange-l-bounces@xxxxxxxxxxxx
[mailto:midrange-l-bounces@xxxxxxxxxxxx] On Behalf Of Jim Oberholtzer
Sent: Wednesday, March 30, 2011 11:06 AM
To: Midrange Systems Technical Discussion
Subject: Re: Cache battery and Raid Controller Design WAS: Re: Rép. :
Question of a Newbie to POWER Systems

True the DASD units will stop spinning. The problem comes with the data
in the cache at that moment. It has not been committed to physical disk
yet. If the cache was lost at that point, then the data in the cache is
lost and the system is corrupted. In a single level storage system,
that's potentially very bad news requiring a reload of the system. So
the smart thing to do is back up the cache with battery until power is
restored, and then commit the cache to disk.

If you had warning, meaning the power goes out, and you have a UPS on
the system, you can with the proper knowledge force the cache to disk,
clearing it. Now everything is on physical storage and loosing cache is
not a big deal. That's basically what happens when the CE replaces the
battery. He/She will force a clearing of the cache to disk and then
replace the battery. It's an easy process although it has to be done
properly.

Jim