sysinst segfaults on Alpha ("file system full") - install help

[John Ames <commodorejohn%gmail.com@localhost>]

Trying to get a NetBSD 9.0 install going on an Alpha 3000 300X
workstation since Tru64 is being a pain in the butt. The install
environment boots and runs, and I can do a bunch of stuff from the
shell with no issues, but the installer itself craps out when
partitioning the disk. I can partition the same disk with disklabel
and create filesystems with newfs totally without issue, so it's not
an issue with the drive - unfortunately, this doesn't give it whatever
magic blessing sysinst needs to recognize the appropriate mount points
automatically, and when I try to use the sysinst partition utility to
do anything (even just set the mount points on already partitioned and
formatted filesystems,) it kills with the following message:

/: write failed, file system is full
[1]   Segmentation fault

Someone else described the same issue at
http://mail-index.netbsd.org/port-sgimips/2003/09/07/0003.html for the
SGI port sixteen-plus years ago :/ So I'm not exactly thrilled about
the chances of a fix coming along, but it's worth asking, I suppose.
One thing I did notice was that /dev/mda0 (the in-memory filesystem
for the installer) ends up very close to completely full, and part of
that is a sysinst.core dump, but I'm not clear on whether sysinst is
dumping core because the filesystem is full, or vice versa. It doesn't
seem like memory constraints should be an issue, though - the box has
160 MB of RAM, way more than the listed minimum.

I think my better shot here is: can I just avoid the sysinst
partitioning utility entirely? I can do everything needed with the
disk from the shell, except apparently chant the proper blessing upon
the resulting partitions. How does sysinst determine which partitions
in the disklabel should map to which mount points in the target
install? Where is that magic documented or stored?