Can not install windows7 when use /dev/sda3 and raw format

[John Wong <johnw@wonghome.net>]

I can not install windows 7 x86, when i use /dev/sda3 and raw disk format.
the windows7 installer can not find the harddisk, no matter what drive i
use (ide/scsi/virtio).

I can install, when i use qcow2.img.

my host system is debian/64bit/sid
uname -a: Linux retro 2.6.32-trunk-amd64 #1 SMP Thu Dec 17 06:29:18 UTC
2009 x86_64 GNU/Linux
qemu-kvm-0.12.1.1
kvm modules come from debian modules package (it shall be 2.6.32)


kvm command like this:

${KVM} -drive if=ide,cache=none,file=${IMG} \
-net nic,vlan=${NUM},model=virtio,macaddr=00:AA:BB:CC:DD:0${NUM} \
-net
tap,vlan=${NUM},ifname="${iface}",script=/etc/kvm/kvm-ifup,downscript=/etc/kvm/kvm-ifdown
\
-localtime -smp 1 \
-usb -usbdevice tablet \
-soundhw all \
-k en-us -monitor stdio \
-mem-path /hugepages \
-cdrom ${CDROM} \
-m 2048 -vga std -boot order=d,menu=off

when i change ${IMG} to ./qcow2.img, then it work.
when i change ${IMG} to /dev/sda3, then it NOT work.
(I'm sure i have read/write permission to /dev/sda3)

please help, and thank you.