RE: disk full guideline

80% guideline is targeted to small installations. What is important is how
much storage is available to system when it needs it. There are many
factors involved: what is storage allocation/free rate, how large is
average allocated segment. how many temporary storage is needed, balance of
storage allocations across disk arms, how many arms you have etc etc. It
depends on configuration and workload characteristics on a particular
system and not easily obtainable without extensive research. Hence simple
rule of thumb - 80%.
It is applicable to large systems in the same way as default QINTER class
timeslice of 2000ms (which was targeted to B10).
I cannot give you simple answer, but with 800+GB on system you should be in
good health well above 90%.


Disclaimer: opinion expressed in this note is entirely my own and in no way
reflects opinion of my employer.

Best regards
    Alexey Pytel



"Dick Lucas" <rlucas@sprynet.com> on 02/04/99 11:59:08 AM

Please respond to MIDRANGE-L@midrange.com

To:   MIDRANGE-L@midrange.com
cc:    (bcc: Alexei Pytel/Rochester/IBM)
Subject:  RE: disk full guideline





Here is the text of a PMR that I just sent to IBM.  Any thoughts or
comments?

Problem Description:
What is the rationale behind the 80% disk full guideline? We consistently
run, without any apparent degradation, in the 90% range, as well as we have
at the 80% level. During certain periods, the percent full approaches 96%,
with no apparent degradation.

We have 170 d/t6607 and 30 d/t6713 raided, at a usable 848 gig. Your
guideline on 20% free equals 160 gig of dasd. Is this a reasonable
guideline? The performance graphs show a difference of 2-3% between average
and maximum.

The holder of the purse is questioning the necessity of buying additional
dasd because of an arbitrary guideline. Please provide me with some
reasonable method of determining what is appropriate.


Dick Lucas



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