RE: Slow AS400 performance

["Christen, Duane J." <dchristen@xxxxxxxxxxxxx>]

The battery is rechargable, (I assume) the warning you get has nothing to do
with the charge on the battery but more to do with it's mean time to
failure. (MTF)

The MTF would be the point in time where the battery is to weak to protect
the cache for a specific time period, not when the battery wont hold a
charge.

Lets say (just pulling numbers out of the air) that the the average MTF is 5
years, and over thousands of tests etc... 4 years was the earliest failure
point. From that data IBM decided that 3 years is when the battery needs to
be replaced to ensure that you don't have a main power failure and battery
to weak to protect the cache.

Duane Christen
  

-----Original Message-----
From: midrange-l-bounces@xxxxxxxxxxxx
[mailto:midrange-l-bounces@xxxxxxxxxxxx]On Behalf Of
Peter.Colpaert@xxxxxxxxx
Sent: Friday, April 21, 2006 1:03 AM
To: Midrange Systems Technical Discussion
Subject: RE: Slow AS400 performance


What I don't understand is why they don't use rechargeable batteries.

That way, when main power is on, the battery is always at full charge, no 
need to replace.

Or am I missing something?

Peter Colpaert
Application Developer
PLI - IT - Kontich, Belgium
-----
Yoda of Borg are we.  Futile is resistance, assimilated will you be.
-----



"Christen, Duane J." <dchristen@xxxxxxxxxxxxx> 
Sent by: midrange-l-bounces@xxxxxxxxxxxx
20/04/2006 22:55
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Subject
RE: Slow AS400 performance






When data gets written to the cache it is considered "written to disk" 
even
though it has not been written to disk yet. When main power is lost the 
data
in the cache is protected by the battery for several days (weeks?). When
main power is restored the controller will write the data to disk and you
won't have lost a thing.
If for some reason the data in the cache is lost you could potentially 
have
to do a full restore on the system which for our main production system
could take 24-48 hours. (I don't know if RAID stripes are stored in the
cache before being written to disk, but that would make a valid cache even
more critical)

IBM has determined that at some point in the life of the battery it will 
not
be able to protect the cache for the desired length of time without main
power, and warns you in plenty of time to replace it. If the battery is 
not
replaced in time the cache is shut off and everything is forced to disk 
when
it reaches the controller causing the performance degradation.


Duane Christen