Win 10 domU can't use disk

[John Nemeth <jnemeth%cue.bc.ca@localhost>]

     I'm having a problem with a fairly new install.  The host is
running NetBSD 9.1_STABLE (with Xen fixes).  It has Xen Kernel
4.13.2nb1 and Xen Tools 4.13.2.  When installing Windows 10 in a
domU, Windows setup reports the disk and the size, but says that
it can't be partitioned or used.  I've tried a variety of ways to
present the disk including LVM, GPT partition, MBR partition, and
raw disk.  The disk line currently has "phy:/dev/rsd1d,ioemu:hda,w".
I have never had problems getting Windows running as a Xen domU
before.  Is anybody else having problems with this particular
combination or have any suggestions?