> Apr 24 04:35:20 flam /netbsd: wd0g: error reading fsbn 237235392 of 237235392-237235455
> (wd0 bn 268435455; cn 266305 tn 0 sn 15)wd0: (id not found)

> can this error be related to discussed quirk?

Probably, try:

dd if=/dev/rwd0c of=/dev/null bs=512 skip=268435454 count=1
dd if=/dev/rwd0c of=/dev/null bs=512 skip=268435455 count=1
dd if=/dev/rwd0c of=/dev/null bs=512 skip=268435456 count=1

If ...54 and ...56 work, but ...55 gets i/o error you probably have the quirk.
Try adding your disk's model number to wd.c as in previous message and the i/o
error will probably go away.  If it doesn't, either your disk really does have
a single bad sector there, or you have some *other* wierd quirk.