Re: Disk sizes and performance

[Larry Bolhuis <lbolhui@xxxxxxx>]

Robin,

 Go here:

 http://www.as400.ibm.com/developer/performance/as4armct.html

 This will give you the information you need re: disk arms.

 As to percentage where performance begins to faulter in my experience
that depends on total storage.  If you have less than 50GB it seems to
begin at 70% and is quite noticable above 80%.  For 50-150 GB it seems
to be more like 70/80.  And over 150GB it seems that you can operate
around 85-90% with little problem.  Note that these are MY
observations.

 HTH - Larry

Robin Sapiro wrote:
> 
> I am looking for some ball park estimates on when to use a greater number of
> small disk drives versus a smaller number of larger disk drives.
> 
> Conventional wisdom is that the more disk arms you have the better the
> performance. Obviously this is directly related to the amount of I/O being
> done on the system. I feel however that there is some point (total disk
> required) at which adding additional disk arms does not have any significant
> improvement on performance and at that point it is more beneficial to use
> larger disks which results in financial savings in the form or lesss $/GB,
> less controllers, less racks etc.
> 
> Any opinions as to what the magic number might be. ie if less than n GB on a
> system, use 4 GB drives. for n-m GB on a system use 8.5 GB drives and for
> greater than m GB on a system use 17 GB drives.
> 
> Also what is the general opinion as to the DASD % utilisation at which I/O
> performance begins to degrade.
> 
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-- 
Larry Bolhuis         | Trivia Question: What famous car carried
Arbor Solutions, Inc  |  the tags:   BDR 529 ?
(616) 451-2500        |
(616) 451-2571 -fax   | Two rules to success in life:
lbolhui@ibm.net       | 1. Never tell people everything you know.
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