Re: New 270.

Hi,

Thanks again for the continuing discussion.
On the web I've found an interesting document called "iSeries Disk Arm
Requirements based on Processor Model Performance"
(to be found here:
http://www-1.ibm.com/servers/eserver/iseries/perfmgmt/pdf/iSarmct.pdf )

It explains why the number of arms are an important factor and has
tables and formulas to calculate diskarm requirements based on model,
feature, disk type, controller type, etc.

Given the 270 I'm looking at (270, 2431, v5r1, Raid-5, 6 4318 disks and
a 2763 Raid controller, I calculate 7.98 or 8 disks.
If I was to replace the 2763 with a 4778 Controller the arm requirement
reduces to 6.098 or 6 disks.

Problem solved I thought, different controller.
However, the hardware and software vendors are quite insistent that a
4778 would be total overkill, that performance using a 2763 would be
fine.

I like the advice because the 2763 costs only half as much as the 4778.
But I'm not all that sure it's the right advice from a performance point
of view. On the other hand, it can be safely assumed that, given the
more capable processor, on average our CPU use would be well below 70%.

Any comments would be most welcome.
Best regards,
Matthias



It contains
> If you get the 17GB drives ( dont see the point of 8GB drives if the price
> is the same ), you will have enough space to save to save file, then save
> savf to tape. In that case, capacity of the tape drive is more important
> than speed. When you SavSys the best tape drive is one that does not need a
> manual load of the next tape. The magstar 3570 ( something like that ) works
> really well, but I am not sure of its price and availabity on the 270.
>
> I am interested in reading what you decide on this.
>
> Steve Richter

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Matthias Oertli   matthias.oertli@mdi.com.au