The battery is the backup. The reason the system stops using cache when it marks the battery dead, is a precautionary measure to ensure that should the system fail, data in the disk cache won't be lost. Basically, it's being cautious.
-----Original Message-----
From: midrange-l-bounces@xxxxxxxxxxxx [mailto:midrange-l-bounces@xxxxxxxxxxxx] On Behalf Of Bryce Martin
Sent: Wednesday, March 30, 2011 7:32 AM
To: Midrange Systems Technical Discussion
Subject: Cache battery and Raid Controller Design WAS: Re: Rép. : Question of a Newbie to POWER Systems
Jim Said....
"Write cache has a massive impact on I/O performance. The more write cache the better. Ask anyone who has lost the batteries on the raid card what happens when write cache goes away. Ugly things happen."
This got me thinking about RAID Card design....
Why the heck isn't the cache batter a backup, not a primary power source?
If the cache batter goes shouldn't the controller still have enough electrical input to keep its cache alive? This just seems like poor design, and a major oversight. Maybe I don't understand hardware design (that is probably the case), but I'm failing to see what the purpose is of the battery vs straight electrical input from the system? I would think you'd want a cache battery in the case of a hardware failure so you don't lose data, but I would think that it should be a backup source....
Thanks
Bryce Martin
Programmer/Analyst I
570-546-4777
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