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

Paul

I think you're right, that the cache is a buffer. But the cache BATtery is there in the event of a power loss - it has nothing to do with normal write-cache behavior. If the system loses power, it can't empty the cache back to disk - so something has to keep the cache activated until power to the disks is restored.

Sound right?

Vern

On 3/30/2011 2:47 PM, Musselman, Paul wrote:

On a running system with nothing much happening, how long does data sit in the cache before it gets written to disk? I'm under the impression that the cache is there as a buffer between the electronic speed of the CPU and 'main memory' and the mechanical speed of a spinning disk. So, theoretically, at some point on a quiet system all data eventually gets written to disk, so (maybe) if all power dropped and the system didn't realize the cache batteries were actually dead you might just get lucky and find your data really was written to disk. So I theorize...

But I wouldn't want to bet my career on a flakey cache battery!

--Paul E Musselman

ps-- I really like our UPS and the diesel generator out back!