Limit maximal tranfer rate to 20MHz

[Doug Ledford]

Ralf Messerer wrote:
> 
> Hi
> I have an Adaptec AHA-294X Ultra with an old external shelf
> from digital (DEC BA356) with 3 Ultra wide disk (40MHz) and 4 fast
> wide disk (20MHz). The external shelf is spezified for maximum
> 20MHz transfer frequency. So I configured the maximum tranfer rate
> of the 3 Ultra wide disks with the Adaptec controller BIOS to
> 40,32, 26.8 and 20 MHz. (What I need is 20MHz because of the shelfs limitation)

Please read things more carefully in the future.  Your shelf is limited to
20MHz operation, and an Ultra Wide disk is *also* limited to 20MHz operation,
but because the disk is wide and transfer 2 bytes of data per cycle, it's
rated at 40MByte/s transfer rate.  There is nothing in your disks or your
controller that operates any faster than 20MHz, so don't even bother rate
limiting them.

As to why the 20 you selected shows up as 10, it's because certain controllers
use different numbers in the SEEPROM to indicate reduced speed capabilities,
and in some cases when the two different versions of controller/BIOS use the
same number to mean two different things, I have to take whichever one I think
is best and use it.  That's what is wrong with the 20 setting on your card. 
I've attempted to make sure that all of the various maximum speed settings
work as they should so that no one has a disk work at less than the maximum
when they are trying for the maximum, and I've had to make trade offs in the
lower speed settings as a result.


-- 

 Doug Ledford <dledford at redhat.com>  http://people.redhat.com/dledford
      Please check my web site for aic7xxx updates/answers before
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