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

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Yep, Paul - data is never meant to stay in the cache on writes - it gets to disk ASAP. The SAP depends on the size of the cache, as well as, I suppose, disk activity - there is a limited number of queues for physical IO at the lowest level - used to be 6.

So data is protected - the only time it might not be is during a crash - when there's no time to flush the cache to disk.

But even if there is a crash, because the battery maintains the viability of the cache, the data will be written out at the next IPL, and once again, all is right with the world.

Vern

On 3/30/2011 4:32 PM, Musselman, Paul wrote:

Vern--

I agree that the battery is only to protect the cache memory.

My question is: won't OS/400 (i) write the cache back to disk during idle moments, so that, on a mostly idle system, won't user data more likely than not still be protected? I remember someone mumbling something about the data in cache being flagged as 'clean' or 'dirty,' clean being written back, and dirty not written back...

Paul E Musselman

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