diff --git a/xenmgr/Vm/Config.hs b/xenmgr/Vm/Config.hs
index f8f83620..a549e317 100644
--- a/xenmgr/Vm/Config.hs
+++ b/xenmgr/Vm/Config.hs
@@ -688,20 +688,26 @@ diskSpec :: Uuid -> Disk -> Rpc DiskSpec
 diskSpec uuid d  = do
   stubdom <- readConfigPropertyDef uuid vmStubdom False
   hd_type <- readConfigPropertyDef uuid vmHdType "ide"
-  return $ printf "'format=raw,backendtype=%s,vdev=%s,access=%s,devtype=%s,script=%s,target=%s'"
-             (cdType stubdom d)
+  return $ printf "'format=%s,backendtype=%s,vdev=%s,access=%s,devtype=%s,script=%s,target=%s'"
+             (format disk_type)
+             (backendType disk_type disk_dev_type)
              (adjDiskDevice d hd_type)
              (enumMarshall $ diskMode d)
              (if (disk_dev_type == "cdrom") then disk_dev_type else "disk")
              (script disk_type)
-             (target disk_type (diskPath d))
+             (diskPath d)
   where
     disk_type = enumMarshall $ diskType d
     disk_dev_type = enumMarshall $ diskDeviceType d
-    cdType stubdom d =
-      case disk_dev_type of
-          "cdrom" -> "phy"
-          _       -> "phy"
+    format "vhd" = "vhd"
+    format "aio" = "aio"
+    format _     = "raw"
+    backendType disk_type disk_dev_type =
+      case (disk_dev_type, disk_type) of
+          ("cdrom", _    ) -> "phy"
+          (_ ,      "vhd") -> "tap"
+          (_ ,      "aio") -> "tap"
+          (_ ,      _    ) -> "phy"
     -- convert hdX -> xvdX if hdtype is 'ahci'
     adjDiskDevice d hd_type =
       case hd_type of
@@ -710,9 +716,6 @@ diskSpec uuid d  = do
     script "vhd" = "block-tap"
     script "aio" = "block-tap"
     script _     = "block"
-    target "vhd" path = printf "vhd:%s" path
-    target "aio" path = printf "aio:%s" path
-    target _     path = path
 
 -- Next section: information about Network Interfaces
 nicSpecs :: VmConfig -> Rpc [NicSpec]