>> viaide0 at pci0 dev 6 function 0
>> viaide0: NVIDIA nForce4 IDE Controller (rev. 0xf2)
>> [snip]
>
> Your very problem, right there. The nForce ATA controllers are
> complete crap. Known issue, go bug 'NVIDIA' about it...

What, exactly, is wrong with the nForce controllers?

My only beef is that, AFAIK, none of the BSDs support NCQ.  :-(
Some brands of SATA disks don't play well with nf4, but that
is easily avoided.  Neither of these problems apply to PATA.