RE: New 270.

Steve,

Your point is well taken.  I was being practical as opposed to
theoretical.  If I was wrong in assuming that the model 400 currently
had six or less drives, then the statement about duplicating the number
of arms was not the best advice.  I would generally add arms until I
reach some boundary, either the capacity of a disk enclosure or RAID
controller.  In the case of a 270, this would be multiples of six.  Once
the boundary is reached, then I would look more seriously at other
options, including adding main storage.

If I could get equal benefit from adding a 17GB drive or 512MB of main
storage, I would add the drive.  A 17 GB drive will cost slightly less
than the memory.  Two drives would cost more than the memory.  There are
other benefits to adding memory and with the recent price decreases; it
makes more and more sense to load up a system with excess memory.

I agree that memory above the minimum will dramatically decrease the
number of physical reads required on any system and can reduce the
number of arms that would be required on a system with less memory.  I'm
not sure that a system with a normal amount of batch throughput would
consider 1 GB of main storage excessive to the point that database pages
would consistently stay in memory.  It seems as though each release of
all operating systems (not just OS/400) requires and uses more memory.
I've worked in technical sales support for the AS/400 and have worked
with a number of sales reps who have tried to lowball the hardware in
order to sell the software.  Sometimes the customers decided to go along
with the rep despite my efforts.  Because of this I have some
unfortunate experience with undersized machines.  I have never seen a
system with 20-30 users doing order entry and other interactive tasks
survive with four drives, even with some excess memory.  I have seen it
work with six.

Mathias, how many drives do you currently have on your machine?

The math on main storage works as follows.  The system 270-2431 has
eight slots which will accept 256, 512, or 1,024 MB memory cards.  A
single card may be installed; after the first they must be in matching
pairs.  The 512 MB card is currently $1,792.  The 1,024 MB card is
$3,584.  The 8.5 and 17 GB drives currently list for $1,400.

Regards,
Andy



> Subject: RE: New 270.
>
> >That said, I would suggest duplicating the number of arms from your
> >model 400 on the 270, assuming performance is adequate (or at least
not
> >I/O-bound).  This may mean that you are swimming in excess capacity,
but
> >it is really the arm-count which will drive your performance rather
than
> >gigabytes of storage.
>
> Andy,
>
> 1GB of main storage is a lot of room.  Shouldnt that decrease non
database
> paging and faulting, resulting in less disk IO ?  Even database paging
> should decrease as the database reads are more likely to be found in
the
> 1GB
> main store space.  To address the disk arm shortage, is it better to
add
> another 17GB drive or 512MB of main store ?
>
> I dont know in practice how this works, but the max main store of the
> 270(2431) is 8GB. At some level of main store disk IO should be
reduced to
> just handling database updates.  That is a lot less actual IO than we
are
> accustomed to seeing.
>
>
> Steve Richter