> $ mount /dev/vnd0a /mnt
> $ ls -l /mnt
> total 4079
> -r--------  1 root  wheel    40448 Jan 31  2001 boot
> -rwxr-xr-x  1 root  wheel  2040053 Jan 31  2001 netbsd
> $ umount /mnt
> $ vnconfig -u vnd0
works for boot-big fine - thanks.

but does not work on rescue-small for example.

browsing this file shows "ustar" after few kilobytes but tar doesn't like
to take it?

maybe
dd if=file bs=some_number skip=1|tar xvf -
?