diff -Nru partman-prep-27ubuntu1/choose_method/prep/do_option partman-prep-27ubuntu1raid1/choose_method/prep/do_option
--- partman-prep-27ubuntu1/choose_method/prep/do_option	2011-01-19 03:05:24.000000000 -0200
+++ partman-prep-27ubuntu1raid1/choose_method/prep/do_option	2016-01-12 09:47:05.000000000 -0200
@@ -10,5 +10,6 @@
 echo prep >"$dev/$id/method"
 echo prep >"$dev/$id/filesystem"
 rm -f "$dev/$id/format"
+rm -f "$dev/$id/mountpoint"
 >"$dev/$id/use_filesystem"
 
diff -Nru partman-prep-27ubuntu1/debian/changelog partman-prep-27ubuntu1raid1/debian/changelog
--- partman-prep-27ubuntu1/debian/changelog	2014-01-27 11:52:05.000000000 -0200
+++ partman-prep-27ubuntu1raid1/debian/changelog	2016-01-12 10:04:34.000000000 -0200
@@ -1,3 +1,18 @@
+partman-prep (27ubuntu1raid1) UNRELEASED; urgency=medium
+
+  * Add basic support for Software RAID devices (LP: #1487365)
+    given a PReP partition created in one of the component devices.
+    - choose_method/prep/do_option: for manual partitioning:
+      remove the mountpoint file, so finish.d/clear_partitions
+      (partman-target) does not consider/mount PReP partitions.
+    - update.d/prep_sync_flag: for guided/auto partitioning:
+      do not set PReP partition flag on Software RAID devices
+      (writes not yet supported by grub2; grub-installer fails);
+      this still requires to re-set the created PReP partition
+      'Use as: PowerPC PReP Partition' after auto partitioning.
+
+ -- Mauricio Faria de Oliveira <mauricfo@linux.vnet.ibm.com>  Tue, 12 Jan 2016 09:53:37 -0200
+
 partman-prep (27ubuntu1) trusty; urgency=medium
 
   * Build for ppc64el.
diff -Nru partman-prep-27ubuntu1/update.d/prep_sync_flag partman-prep-27ubuntu1raid1/update.d/prep_sync_flag
--- partman-prep-27ubuntu1/update.d/prep_sync_flag	2011-01-19 03:05:24.000000000 -0200
+++ partman-prep-27ubuntu1raid1/update.d/prep_sync_flag	2016-01-12 09:49:00.000000000 -0200
@@ -36,6 +36,19 @@
 done
 close_dialog
 
+# Do not set PReP partition flag on Software RAID devices.
+# (grub2 does not support writes to it; grub-installer fails)
+device=
+if [ -f device ]; then
+	device="$(cat device)"
+fi
+
+if echo "$device" | grep -q '/dev/md'; then
+	logger -t prep_sync_flag "Not setting the PReP partition flag on Software RAID device '$device' (writes not yet supported by grub2)"
+	method=
+	has_prep=yes
+fi
+
 if [ "$method" = prep ] && [ "$has_prep" = no ]; then
 	open_dialog SET_FLAGS $id
 	write_line "$flags"