RE: Cache Batteries: When Concurrent Maintenance Isn't...

Hi all,

i changed a lot of cache batteries (300+) in the last years at our own machines and at customer boxes. If the controller
is concurrently maintenantable, the procedure leaves the write cache disabled for 2-3 minutes, depending on how
fast you do the job. This will lead to the performance degradations as described.

There are some issues one must take care of:
- always run the "disable write cache" procedure, even if the disks already are degraded
- this also is important on the older controllers not concurrently maintainable
- do not buy cheap batteries from sources not known! On the new controller batteries you often
find a sticker with the date the cache battery should not used any longer

I tried to recharge older controller batteries (2778, 2748 etc), but this was not successfull on all attempts;
it is better to spend 30$ for a checked battery which has not been in a storage for years.

Oh - and i never got a battery which needed to be recharged; which type of controller was this? Until now,
the "start cache" function always worked as expected - started the cache 2 seconds later.

-h


-----Original Message-----
From: midrange-l-bounces@xxxxxxxxxxxx [mailto:midrange-l-bounces@xxxxxxxxxxxx] On Behalf Of DrFranken
Sent: Sunday, May 20, 2012 1:04 AM
To: Midrange Systems Technical Discussion
Subject: Re: Cache Batteries: When Concurrent Maintenance Isn't...

Thanks for sharing your experience!

It is true ladies and gentlemen that the lack of cache can in fact have a severe impact on performance. As with all things computing YMMV but safe to say that it's very rare when I suggest to a customer that it truly is OK to replace batteries while the system is running actual production workloads. Rarely a customer doesn't even notice but the only way to know if this will 'hurt' is to do it and then if it hurts, that sucks.

It has been my experience that the recharge time is significantly less than you saw but just like a UPS if the battery isn't charged there is no backup.