diff --git a/src/cmd-buildextend-metal b/src/cmd-buildextend-metal
index 162bdf81c8..f229faebbb 100755
--- a/src/cmd-buildextend-metal
+++ b/src/cmd-buildextend-metal
@@ -234,20 +234,16 @@ if [ -n "${ref_is_temp}" ]; then
     ref_arg=${commit}
 fi
 
-target_drive=("-drive" "if=virtio,id=target,format=${image_format},file=${path}.tmp,cache=unsafe")
+target_device_opt="scsi-disk,drive=target,wwn=0x2a"
 # we need 4096 block size for ECKD DASD and (obviously) metal4k
 if [[ $image_type == dasd || $image_type == metal4k ]]; then
-    device_type=virtio-blk
-    if [[ $image_type == dasd ]]; then
-        device_type=virtio-blk-ccw
-    fi
-    target_drive=("-drive" "if=none,id=target,format=${image_format},file=${path}.tmp,cache=unsafe" \
-                    "-device" "${device_type},drive=target,physical_block_size=4096,logical_block_size=4096,scsi=off")
+  target_device_opt="${target_device_opt},physical_block_size=4096,logical_block_size=4096"
 fi
+target_drive=("-drive" "if=none,id=target,format=${image_format},file=${path}.tmp,cache=unsafe" \
+              "-device" "virtio-scsi-${devtype},id=scsitarget" "-device" "${target_device_opt}")
 
 runvm "${target_drive[@]}" -- \
         /usr/lib/coreos-assembler/create_disk.sh \
-            --disk /dev/vda \
             --buildid "${build}" \
             --imgid "${img}" \
             --grub-script /usr/lib/coreos-assembler/grub.cfg \
diff --git a/src/create_disk.sh b/src/create_disk.sh
index 192c17d11d..b499472b48 100755
--- a/src/create_disk.sh
+++ b/src/create_disk.sh
@@ -37,6 +37,7 @@ run as part of 'coreos-assembler build'.
 EOC
 }
 
+disk=
 rootfs_size="0"
 boot_verity=0
 rootfs_type="xfs"
@@ -73,7 +74,25 @@ udevtrig() {
 
 export PATH=$PATH:/sbin:/usr/sbin
 arch="$(uname -m)"
-disk="${disk:?--disk must be defined}"
+
+if [ -z "${disk:-}" ]; then
+    # hex 0x2a = 42 in decimal; this is set in cmd-buildextend-metal.
+    # We use the WWN as an unambiguous way to identify our target disk,
+    # independent of other devices attached to the VM (caches, etc.)
+    wwn=000000000000002a
+    for dev in /sys/block/*; do
+        if grep -F -e "${wwn}" "${dev}/device/wwid" 2>/dev/null; then
+            disk="/dev/$(basename ${dev})"
+            break
+        fi
+    done
+    if [ -z "${disk:-}" ]; then
+        echo "failed to find disk with wwn ${wwn}" 1>&2
+        bash
+        exit 1
+    fi
+fi
+
 buildid="${buildid:?--buildid must be defined}"
 imgid="${imgid:?--imgid must be defined}"
 ostree="${ostree:?--ostree-repo must be defined}"
diff --git a/src/supermin-init-prelude.sh b/src/supermin-init-prelude.sh
index 8b2eb78088..8f5cd87212 100644
--- a/src/supermin-init-prelude.sh
+++ b/src/supermin-init-prelude.sh
@@ -30,7 +30,7 @@ if [ -L "${workdir}"/src/config ]; then
     mount -t 9p -o rw,trans=virtio,version=9p2000.L source "${workdir}"/src/config
 fi
 mkdir -p "${workdir}"/cache /host/container-work
-cachedev=$(blkid -lt LABEL=cosa-cache -o device)
+cachedev=$(blkid -lt LABEL=cosa-cache -o device || true)
 if [ -n "${cachedev}" ]; then
     mount "${cachedev}" "${workdir}"/cache
 else