How to Force UDMA100 Mode on Boot?

Mark Kane mark at
Tue Aug 16 08:35:38 GMT 2005

Chuck Swiger wrote:
> Your BIOS ought to have a setting which throttles this down.

 From what I see in the BIOS it just says "DMA Mode" and then Enabled or 
Disabled. Unfortunately it doesnt look like any drive-specific options 
to choose which speed.

> 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

Everything seems fine with all the drives until I try to start to 
transfer data between them at 133 mode. So I think that rc entry you 
suggested would be perfect, since that would execute before I would 
start transferring any files.

Thanks :)


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