>> What goes wrong?  (I'm having trouble imagining a failure mode that
>> would break booting from the disk but would permit NetBSD to use the
>> disk once booted.)
> I am in this situation.  Friend has a Sparcstation SLC which used to
> run NetBSD, but it got somewhat broken (don't know the cause) and now
> if we try to boot BSD from disk, it prints only some error like
> "Memory access not aligned", don't remember exactly.

Have you tried reinstalling the bootblocks on the disk?  This can be
caused by anything that corrupts the bootblocks (including the
second-stage booter normally kept in /boot - and that file is not an
ordinary file in some respects; for example, copying it and trying to
use the copy will not work until you reinstall the first-stage
bootblocks).

> But it can boot the kernel from a tape, an then it's possible to
> access the disk normally.  So I would like to boot a kernel from a
> tape (or from net), but to mount sd0a as the root filesystem, and I
> did't know how to do it.

As I gather you've already picked up from the discussion, boot with -a,
or use a kernel explicitly configured "root on sd0a".

> Your suggestion with configuring the root fs to the kernel is
> helpful, but how do I make the resulting kernel bootable from tape?
> I tried dd-ing in to the tape, but it did't work.

I don't know; I've never tried.  It could be that the existing
bootblocks will work untouched; it could be they need tweaking; it
could be they need serious overhauling.  It might even depend on what
sort of tape drive you have.  I would not expect just dding the kernel
to tape without any headers or anything to work (I might try it but
would not be surprised if it didn't work).

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