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

Bryce

Interesting question - seems to me that the cache battery is a backup - it preserves anything in the cache in the event of a power outage. The system could and probably does use the regular power of the system during normal operations.

The matter of slowing down when the cache battery's life is running out - I think this happens for a different reason - if the battery can't keep data in the cache, then you can't rely on the cache. So writes have to be done synchronously, not through the cache, because the backup is not trustworthy. This slows it down.

I've not thought of this at all, so my ideas can be far off base!

Vern

On 3/30/2011 7:32 AM, Bryce Martin wrote:

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
--- This message (including any attachments) is intended only for the use of the individual or entity to which it is addressed and may contain information that is non-public, proprietary, privileged, confidential, and exempt from disclosure under applicable law. If you are not the intended recipient, you are hereby notified that any use, dissemination, distribution, or copying of this communication is strictly prohibited. If you have received this communication in error, please notify us and destroy this message immediately. ---