Hello Zbigniew,

  ZB> I would to connect additional HDD (with older
    > installation of NetBSD) to copy some files from.
    > Surprisingly, such operation does turn my (formerly)
    > wd0 into wd1 - while system does want to see the new
    > one as wd0. In a consequence, i've got "unexpected
    > inconsistency", "run ffsck manually", "single-user
    > mode (ro)" and so on.

From your mention of wd0 and wd1, I am guessing that you are
using ATA ("IDE") disk drives and that they are attached to
the same channel (they're on the same physical cable).  What
you are seeing might be a consequence of "cable select":
where the cable somehow determines which is the primary and
which is the secondary drive.  I can think of a couple of
other reasons why you might see this odd behaviour, neither
of which are NetBSD's fault. The disk drive that was in your
computer before you added the old one: is it jumpered as the
primary drive (on that channel), the only drive, the
secondary, or "cable select"?  What about the drive that you
have just added?

Czesc,
  - Andy Ball.