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

[DrFranken <midrange@xxxxxxxxxxxx>]

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.

    - Larry "DrFranken" Bolhuis

On 5/19/2012 6:15 PM, Musselman, Paul wrote:
> Shoulda known better.  But the "Replace Your Cache Batteries Soon" message -says- the replacement is OK to do concurrently.
>
> However.  It should be done at a "quiet" time-- like 3 AM when no one is on the system!
>
> The cache is disabled during the switch.  This was not a surprise.   The hardware people said there might be a performance hit while the cache is disabled.
>
> OK, like when a RAIDed disk has gone bad and the system has to build data on-the-fly performance hit?
>
> NO!  The "performance hit" is SEVERE!  Like driving your car into a brick wall at 70 MPH is severe.  Like being eaten by a shark is severe.
>
> If "Normal" is Niagara falls during rainy season, the degraded performance is like Death Valley in the middle of August.  Like watching paint dry.  Grass grow.  Molasses running uphill in January.
>
> Disk access slowed to a c........r..............a..............w..................l...  Every job was probably reaching end of time slice and there was probably thrashing going on.  Not to mention the thrashing users would have liked to give IT!
>
> The replacement batteries are re-chargeable, but do NOT arrive with a full charge!  And even though the CE took the option to re-activate the cache, it remains disabled until the batteries are recharged.  The hardware people and the CE said it would take 'about an hour' until they reached full charge.
>
> *sigh*
>
> Talking with the -software- people during the fun, -they- said it could be 6-8 hours!
>
> *AARRRGGHH*
>
> Took about 3 hours for us.
>
> ==Paul E Musselman
> PaulMmn@xxxxxxxxxxxxx