--- nova-2012.1/nova/virt/libvirt/utils.py.orig	2012-06-04 10:55:00.000000000 +0200
+++ nova-2012.1/nova/virt/libvirt/utils.py	2012-06-04 10:53:51.000000000 +0200
@@ -124,6 +124,10 @@
         execute('mkswap', path)
     else:
         args = ['mkfs', '-t', fs]
+		# Add -F for ext3 and ext4 filesystems
+		# to force action on non-block device
+		if fs in ['ext3', 'ext4']:
+			args.extend(['-F'])
         if label:
             args.extend(['-n', label])
         args.append(path)