How to Force UDMA100 Mode on Boot?

Kent Stewart kstewart at
Tue Aug 16 04:51:16 GMT 2005

On Monday 15 August 2005 07:38 pm, Chuck Swiger wrote:
> Howdy--
> Mark Kane wrote:
> [ ... ]
> > I know about atacontrol to set it manually, but I'd like to set
> > UDMA100 mode automatically on boot since I have 5 hard drives. I
> > also know the sysctl hw.ata.ata_dma, but that doesn't say anything
> > about using 100 vs 133.
> Your BIOS ought to have a setting which throttles this down.
> Simply changing in within FreeBSD might be a little late, since the
> system has to boot far enough to get to that, or you might run some
> other OS on the machine one fine day.  Anyway, consider:
> touch /etc/rc.local
> echo "/sbin/atacontrol mode ..." >> /etc/rc.local

There used to be a Maxtor utility that would set the maximum ATA rate on 
Maxtor ATA drives. I had one of those motherboard with a broken 
Southbridge and that was the easy way out until I replaced the 
motherboard with a good one. If you aren't using Maxtor's, you can look 
for a utility to do what the Maxtor utility did.


Kent Stewart
Richland, WA

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