> The disk works without any problems
> under FreeDOS and Linux. Is SiI3112 driver in NetBSD broken?

3112 work fine for me under NetBSD-4_RC5

satalink0: Silicon Image SATALink 3112 (rev. 0x02)

wd2 at atabus2 drive 0: <ST3320620AS>
wd2: quirks 2<FORCE_LBA48>
wd2: drive supports 16-sector PIO transfers, LBA48 addressing
wd2: 298 GB, 620181 cyl, 16 head, 63 sec, 512 bytes/sect x 625142448 sectors
wd2: 32-bit data port
wd2: drive supports PIO mode 4, DMA mode 2, Ultra-DMA mode 6 (Ultra/133)
wd2(satalink0:0:0): using PIO mode 4, Ultra-DMA mode 6 (Ultra/133) (using DMA)

wd3 at atabus3 drive 0: <ST3320620AS>
wd3: quirks 2<FORCE_LBA48>
wd3: drive supports 16-sector PIO transfers, LBA48 addressing
wd3: 298 GB, 620181 cyl, 16 head, 63 sec, 512 bytes/sect x 625142448 sectors
wd3: 32-bit data port
wd3: drive supports PIO mode 4, DMA mode 2, Ultra-DMA mode 6 (Ultra/133)
wd3(satalink0:1:0): using PIO mode 4, Ultra-DMA mode 6 (Ultra/133) (using DMA)

-- 
Best regards, Aleksey Cheusov.