> It seems the disklabels created by NetBSD/alpha and NetBSD/i386
> aren't compatible?

Apparently not, based on your tests.  I suspect fdisk-style
partitioning and i386 BIOS goop of being at least partly at fault.
Note that your i386 c partition begins at offset 108, meaning that your
disklabel will be stored somewhere around sector 108; the alpha port
expects it in sector zero.

If you don't expect to make it bootable, you might be able to make the
i386 disklabel live at sector zero by making the NetBSD fdisk-style
partition start at offset zero.  I don't know if you'll get too many
different things all trying to use the beginning of the disk then....

> I thought the different ports of NetBSD would all(?) use ffs file
> systems

Yes, I think all NetBSD ports support ffs. :-)  But your problem here
is not filesystems but partitioning.

> and it would be possible for them to mount each others partitions.

Once the _find_ each others' partitions, they probably will be able to
mount them.  If you use my bsdlabel program to read the "foreign"
partitions and use S to set the in-core disklabel without changing the
on-disk disklabel, you probably will then be able to access the drive's
partitions.  (Just make sure you suspend bsdlabel rather than exiting
it; you want to keep the drive open to keep the in-core label valid.)

ftp.netbsd.org:/pub/NetBSD/misc/mouse/hacks/bsdlabel.c

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