Question 1:

dd if=/dev/rwd0c count=161507 bs=1512k of=/dev/null
dd: /dev/rwd0c: Input/output error
160465+0 records in
160465+0 records out
248446033920 bytes transferred in 6623.766 secs (37508274 bytes/sec)

Looking in /var/log/messages:

/netbsd: wd0: transfer error, downgrading to Ultra-DMA mode 2
[ more read errors ]
/netbsd: wd0: transfer error, downgrading to Ultra-DMA mode 1

Is there a way to get wd(4) to upgrade the mode back without rebooting?
I don't see anything in wd(4) or atactl(8) man pages.

Question 2:

dd if=/dev/zero of=/dev/rwd0c count=161507 bs=1512k

dd: /dev/rwd0c: Input/output error
160466+0 records in
160465+0 records out
248446033920 bytes transferred in 37890.490 secs (6556949 bytes/sec)

I was expecting to see a disk write error logged in /var/log/messages,
but there is nothing?

(I am assuming that /dev/zero never generates an I/O error.)

NetBSD 2.0.2
The WD_QUIRK_FORCE_LBA48 128MB quirk is patched and verified working.

Disk is a brand new Seagate 250 GB 7200.8 SATA.
An identical model disk connected to the other port of the same
controller has been working fine for 2.5 months.
The write cache is turned off on both disks.

Alpha 164lx

satalink0: Silicon Image SATALink 3512 (rev. 0x01)
satalink0: port 0: device present, speed: 1.5Gb/s
wd0 at atabus0 drive 0satalink0: port 1: device present, speed: 1.5Gb/s
: <ST3250823AS>
wd0: drive supports 16-sector PIO transfers, LBA48 addressing
wd0: 232 GB, 484521 cyl, 16 head, 63 sec, 512 bytes/sect x 488397168 sectors
wd0: 32-bit data port
wd0: drive supports PIO mode 4, DMA mode 2, Ultra-DMA mode 6 (Ultra/133)
wd0(satalink0:0:0): using PIO mode 4, Ultra-DMA mode 6 (Ultra/133) (using DMA data transfers)