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Hardware, Battery backed Cached RAID

Posted on 2012-04-11
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Last Modified: 2012-06-27
Is a battery backed RAID secure enough for Database work

How does recovery work, if the machine loses power, and only the battery is up and saving the cache, how does the machine recover when its powered up.
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Question by:Los Angeles1
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Perarduaadastra earned 500 total points
ID: 37833179
The battery maintains the contents of the RAID controller cache so that any delayed writes are preserved in the event of a power outage, and written to disk when the machines comes back up again. This avoids data corruption caused by the system thinking that data is present on the disk when it actually disappeared with the power...
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by:Perarduaadastra
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Sorry, didn't answer the first question!

By secure, do you mean reliable? If so, RAID controller battery backup is another layer of data protection, though most servers, especially mission-critical ones, will have their own UPS protection against power loss and probably redundant PSUs as well. The battery backup of the RAID controller is most useful in scenarios where the wrong power cable is pulled by mistake in a densely populated rack during maintenance - easily done!
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by:andyalder
ID: 37833377
Most battery backed write cache lasts 72 hours, after that the battery goes flat and the cache is stale. For longer outages you may be able to have flash backed write cache, that has a small battery or maybe a supercapacitor to power it for the few seconds it takes to copy the RAM to a flash chip. It's possible that the cache will fail of course, or the controller itself could fail, not much you can do to cover that possibility.
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