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Drive Array Accelerator Batteries: discuss

 
ken M_2
Occasional Contributor

Drive Array Accelerator Batteries: discuss


Given the disk performance issues experienced when Drive Array Accelerator Batteries fail (disk queue times), I assume drive accelerator batteries are associated with increasing drive performance.

Anyone know the logic of using a battery instead of direct current?

The traditional purpose of batteries is to save configurations or keep cache memory safe in the event of a unexpected system crash, but I don't understand why they are important for the efficient performance of a running machine.
4 REPLIES
Blazhev_1
Honored Contributor

Re: Drive Array Accelerator Batteries: discuss

Hi,

what improves performance and "adds extras" to your performance is not actually the battery, but the cache module(the whole component is called Battery-Backed Write Cache).

When you wan to write data from/to the hard drives, then continues data is saved in the cache and then at once sent to the cotroller. The battery is there, so that if a power is suddenly removed from the server , the data saved in the cache module is not lost.

F.e. Example you have 10MB data in the cache ready to be written to the drives, then power is removed. If there is no battery , these 10MB are lost. battery has life 72 hours - if you return the power. then "POST 1792 - Valid Data found in array accelerator" is shown indicating this.

The firmware of the SA controllers disables the cache if there is no battery(failed). The actual difference in performance is because the cache is disabled.(Array Accelerator Status Disabled)

Think there was a document, will post if
I find it.

If you have questions - ask :)
Pac
Blazhev_1
Honored Contributor

Re: Drive Array Accelerator Batteries: discuss

can't find the document I was searching for, but here some documents taht may help you understand the BBWC

Page 9&10 :

http://h20000.www2.hp.com/bc/docs/support/SupportManual/c00687518/c00687518.pdf

and partially :

http://h20000.www2.hp.com/bizsupport/TechSupport/Document.jsp?lang=en&cc=us&objectID=c00818421&prodTypeId=15351&prodSeriesId=455149

Maybe this :

"Data in the controllerâ s write cache is written to disk later, at an optimal time for the controller. While the data is in cache, it is protected against memory chip failure by error checking and correction (ECC) DRAM technology and against system power loss by the integrated battery backup mechanism. Smart Array controllers avoid the risk of data loss by ensuring that the battery backup is present before enabling write-back cache. Hard drives provide an option to enable write-caching that is not battery backed. HP advises against enabling hard drive write cache because a power or equipment outage could result in data loss."

Pac
Torsten.
Acclaimed Contributor

Re: Drive Array Accelerator Batteries: discuss

The short version:

no battery = no write cache = lower performance

Hope this helps!
Regards
Torsten.

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ken M_2
Occasional Contributor

Re: Drive Array Accelerator Batteries: discuss

OK, mkes sence