GPT, wedges and RAID-1 on new server with NetBSD 7

[Gerard Lally <gerard.lally%gmail.com@localhost>]

Later this month I will be replacing a dedicated single-disk 120GB SSD
server with a 2 x 2TB SATA server. I would really like to put NetBSD 7
on RAID-1 here; I've had it running very nicely on the single disk
server for months (with thanks to Manuel Bouyer for the Dedibox
instructions).

The trouble is, I've been installing and re-installing NetBSD 7 on
Virtualbox with two virtual disks of 8GB each to get at least the RAID
part right before I make the move on real hardware but I've had no
luck booting the system whatever.

This is how I have been doing it so far:

1) Boot from amd64 CD
2) Select "Utility menu"
3) Select "Partition disk"
4) Format the already-existing wd0a as RAID; do the same for wd1a
5) Now select "Create software RAID", with wd0a and wd1a as disks,
RAID level set to 1 and sectPerSU set to 128
6) Save changes, as instructed
7) Wait for parity re-write to finish

Next step is where I get confused. I now have to create partitions for
RAID. The parity re-write created raid1a with type 4.2BSD which takes
up the whole 8GB.

If I want separate / swap and /home, I presume I should delete raid1a
and create raid1a, raid1b and raid1e instead (by clicking on its
parent raid1 and selecting "Edit BSD partitions")?

I create these and proceed with installation as normal, selecting
raid1 as the available disk on which I want to install NetBSD. But
each time I do this I get the dreaded error "FATAL: No bootable medium
found! System halted."

Where am I going wrong? One thing I note is that I am not asked at any
point to install bootcode to the disks as I would be with non-RAID
setups.

If it's not possible to do this with sysinst is it at least possible
to do it by dropping to a shell? Ideally I would like to use GPT with
the RAID-1 setup as well, since I will be on 2 x 2TB disks and I
anticipate this getting bigger, not smaller in years to come. I have
successfully set up NetBSD with GPT by dropping to a shell but I don't
know where to add RAID into that mix.