Re: High DASD utilization

[Pete Hall <peteh@xxxxxxxxxx>]

At 09:27 AM 7/7/98 -0700, Ken Graap wrote:
>Several years ago I had a conversation with IBM about the long term
>affect of running at 95% plus AUX Storage utilization on an AS/400. I
>can't remember the conversation exactly, but I do seem to remember that
>there are some dire consequences of having auxiliary storage remain very
>high for extended periods of time.
>
>The part I seem to have retained in my brain was that eventually the
>system would have to be completely restored.... Yikes!
>
>Does anyone have any knowledge of what the consequences are of running
>between 95-99% AUX Storage utilization for months on end might be?

Ken,

AFAIK, this is still true. When you exceed about 70%, you start to pay a 
performance penalty, because the system must put more effort into finding 
places to stuff new data. During normal operation however, the system must use 
some DASD for work areas, paging, etc. This space gradually grows over time. 
When you approach 100%, you risk having the system require more space for 
internal use when none is available. If this happens, the system will crash, 
and you will be forced to IPL. The (exteeeeended) IPL process will recover the 
used work space, and all will be relatively well. If however, you start writing 
records or creating objects and actually use up all of the available disk 
storage, and the system has not accumulated a sufficient amount of recoverable 
space, you may not even be able to IPL. If this happens, you will need to 
scratch and restore everything. Depending on the amount of DASD on your system, 
95%, while not good, may or may not actually be dangerous. I would hit !
the 
big red flapper switch before I reached 99% though. Those 96 hour days are not 
a lot of fun.

Pete


Pete Hall
peteh@inwave.com 
http://www.inwave.com/~peteh/

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