I started by booting my virtual machine the obvious way - expose both drives to the VM, and select to boot Plan 9. Trouble comes up when I miss the time-out though: it tries to boot linux again from the same disk it's already running on - a risky proposition at the best of times.
The next fix to try was to use the secondary drive as the primary drive of the VM, but this falls apart because fossil encodes the partition identifier on the file system itself.
The simple solution (thanks to Takeshi Yamanashi) was to build a small virtual hard drive in VMWare, and to pre-load it with a master boot record and 9fat file system; I have to remember to update kernels in two places (there and on my secondary drive for cold- bootin) but it works like a charm.
To make such a file system, use VMWare to add a new (small! 0.1Gig is plenty!) disk to a Plan 9 virtual machine that already boots. Boot your vm, and check what the new drive is called:
prompt% ls -d /dev/sd?? /dev/sdC0 /dev/sdC1 /dev/sdD0
In my case the new drive was /dev/sdC1 - corresponding to ide0:1 in my vmware machine.
Now you have to give that partition a master boot record, fdisk it, prep it, and format it. Before going any further, mount your dos partition:
or else you'll have to go digging for 9load, a kernel, and your plan9.ini if you wait until you've built the 9fat we're going to put together (you can mount the 9fat drive later, but the 9fat: script fails when there is more than one 9fat partition available)
Now we can start prepping the new virtual partition:
If you hit the wrong partition with these commands you *will* do damage to your system. In my example I'm using sdC1 - that might not be yours!
So to start we give the new disk an MBR:
prompt% disk/mbr -m /386/pbs /dev/sdC1/data
Then we fdisk it, making one large plan9 partition:
prompt% disk/fdisk -baw /dev/sdC1/data
Next we prep it to make a 9fat sub-partition:
prompt% disk/prep -bw -a9fat /dev/sdC1/plan9
And finally we format the new partition, telling format to add the 9load, kernel, and plan9.ini files. I used the files from my working boot partition; the order you specify these in matters - 9load has to be first. See prep(8) for the other options:
prompt% disk/format -b /386/pbs -d -r 2 /dev/sdC1/9fat /n/9fat/9load /n/9fat/9pcf /n/9fat/plan9.ini
You can, of course, use whatever kernel you want - 9pcf just happens to come with the distribution. You can also add more files to the list (including more kernels), although once the new 9fat fs is built, you can just mount it and copy more files there.
I hope this works for you as well as it did for me.