How to Force UDMA100 Mode on Boot?

Chuck Swiger cswiger at
Tue Aug 16 02:38:32 GMT 2005


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


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