Disk operation fails since 5.3 for newer harddisks and older motherboards

[Rob]

Hi,

I had several PCs running 4.10, when I gradually
upgraded them to 5.3. Occassionally I had great
difficulties, which appeared to be somehow related
to the motherboard, the harddisk and the UDMA
selection...... or something like that (sorry, I'm
not an expert on this!).

All PCs have just simple harddisks; no such things as
RIAD, SCSI, but simply IDE connected disks.
 
Emperically, I have come to following conclusions:

Big problems occurred always when the motherboard is
older (supporting only UDMA66 or less), and the
harddisk newer (being able to handle UDMA100). When
going ahead with regular FreeBSD 5.3 installation,
this ended with kernel panic at bootup after
installation, or, on another PC, with odd behavior
after boot (e.g. X kept crashing for no reason).

These problems always got solved by manually adding
to /boot/loader.conf:   hw.ata.ata_dma="0"

This fix also implies, that the harddisk seemed to be
forced to operate at PIO4 speed, although UDMA66
should be possible in this case.

Apparently it's the motherboard-harddisk speed
mismatch, which FreeBSD 5.3 cannot handle decently.

When motherboard and harddisk speeds match (both
new, or both old), there are not such problems as
mentioned above.

Any other people with this experience?

Any idea why such problems suddenly pop up with 5.3?

Regards,
Rob.

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