How to Force UDMA100 Mode on Boot?

Mark Kane mark at
Tue Aug 16 23:14:30 GMT 2005

jason wrote:
> I checked the links and saw no dmesg or drive models for all drives.  I
> can tell you UDMA 133 was not an official spec, a least at first.  It
> was a maxtor only thing, and not all chipsets handled it.  Basically
> maxtor tightened the timings on the ide cable signals to squence extra
> data.  If you have new and old drives, plus different brands I would not
> expect to run at 133 speeds.  I don't care to look it up now, but you
> may want to find out if any other drive manufactures support the 133
> spec today.  Also there are load and signal degregation issues with to
> think about with longer cables.  If you have a full tower case with the
> longest cables you can buy you won't get max speeds even at the 133
> setting.  If you know someone whos works in a pc rpair shop you could
> ask them what cable length does to drive speeds.  I am told if you want
> to copy drives for customers you want to get a good cable, but only with
> 1 device per cable and get it as short as possible.  A 2 inch cable will
> dramatically shorten the time to copy whole drives compared to a 16 inch
> cable.

Well now I can't even get two drives on the same channel to mount 
together. If one is mounted and I try to mount the other one on the same 
channel, the other gets immediate DMA_READ problems and then failures. 
This is trying two brand new drives with brand new cables.

If I eliminate one of the drives and run one on each channel, they all 
work fine together. I'm not sure if that rc.local trick that was 
suggested would work now. I don't know if drives get mounted before 
rc.local would get executed or not.

Going to have to bring back my thread on the errors.


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