The IBM System Storage DS4000 cache battery provides valuable backup for the controller cache in the event of a subsystem power failure. The battery will allow the controller cache to be de-staged (i.e. written to disk) safely and ensure data remains consistent.
In older levels of controller firmware, these batteries were set to notify regarding an impending expiration at 36 months followed by cache disable action by the microcode at 39 months. When the cache disables, you could experience performance degradation since the controller's high speed cache is no longer in use.

IBM now state that in fact these DS4000 batteries can last well past 62 months and in controller firmware 6.60.02.00 and onwards a notification is now set to occur at 62 months followed by the cache disable action by the microcode a little after ten years.

I have found that when logging calls with IBM for the "Battery Nearing Expiration" notification, if the firmware is below 6.60.02.00 they simply tell me to reset the battery age to zero. Of course if the battery has actually failed then this would be replaced as usual under maintenance.

It's worth noting that there are no diagnostics to trigger the expiration notification and the date is purely hardset in microcode.

All this information was obtained from IBM retain tip H193840.
For more information contact Emily on 0115 951 9666 or visit the Centiq website, Nottinghams Premier IT Specialists company.

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