Adding disk to Windows XP guest

I've got a Windows 8 computer running Hyper-V. I've created a Windows XP VM and am trying to attach another disk. I've added both a VHD (created using powershell) and a physically attached (e-SATA) disk. I've added the disks while the VM was both on and off. I also tried changing the location (the SCSI ID). In the VM, I've used Disk Manager to rescan disks and diskpart to list disks and volumes. 

The second disk just isn't showing up in XP. What gives?

Thanks.