Set cache mode for target installation disk to unsafe for better
performance.
Index: virt-manager-2.2.1/virtinst/install/installer.py
===================================================================
--- virt-manager-2.2.1.orig/virtinst/install/installer.py
+++ virt-manager-2.2.1/virtinst/install/installer.py
@@ -422,11 +422,22 @@ class Installer(object):
                 guest.memory) = data
 
     def _get_install_xml(self, guest, meter):
+        # At install time set the target disk to 'unsafe' for
+        # better performance if the target is not a block device
+        saved_cache = "None"
+        if guest.devices.disk:
+            target_disk = guest.devices.disk[0]
+            saved_cache = target_disk.driver_cache
+            if target_disk.type != DeviceDisk.TYPE_BLOCK and target_disk.driver_io != "native":
+                target_disk.driver_cache = DeviceDisk.CACHE_MODE_UNSAFE
+
         data = self._prepare_get_install_xml(guest)
         try:
             self._alter_bootconfig(guest)
             self._alter_install_resources(guest, meter)
             ret = guest.get_xml()
+            if saved_cache != "None":
+                target_disk.driver_cache = saved_cache
             return ret
         finally:
             self._remove_install_cdrom_media(guest)