diff --git a/nova/tests/unit/virt/xenapi/test_vm_utils.py b/nova/tests/unit/virt/xenapi/test_vm_utils.py
index e15cc53..a777fcc 100644
--- a/nova/tests/unit/virt/xenapi/test_vm_utils.py
+++ b/nova/tests/unit/virt/xenapi/test_vm_utils.py
@@ -189,7 +189,7 @@ class GenerateConfigDriveTestCase(VMUtilsTestBase):
                       '-publisher', mox.IgnoreArg(), '-quiet',
                       '-J', '-r', '-V', 'config-2', mox.IgnoreArg(),
                       attempts=1, run_as_root=False).AndReturn(None)
-        utils.execute('dd', mox.IgnoreArg(), mox.IgnoreArg(),
+        utils.execute('dd', mox.IgnoreArg(), mox.IgnoreArg(), mox.IgnoreArg(),
                       mox.IgnoreArg(), run_as_root=True).AndReturn(None)
 
         self.mox.StubOutWithMock(vm_utils, 'create_vbd')
diff --git a/nova/virt/xenapi/vm_utils.py b/nova/virt/xenapi/vm_utils.py
index c8fdc52..9bbf173 100644
--- a/nova/virt/xenapi/vm_utils.py
+++ b/nova/virt/xenapi/vm_utils.py
@@ -138,6 +138,7 @@ MBR_SIZE_BYTES = MBR_SIZE_SECTORS * SECTOR_SIZE
 KERNEL_DIR = '/boot/guest'
 MAX_VDI_CHAIN_SIZE = 16
 PROGRESS_INTERVAL_SECONDS = 300
+DD_BLOCKSIZE = 65536
 
 # Fudge factor to allow for the VHD chain to be slightly larger than
 # the partitioned space. Otherwise, legitimate images near their
@@ -1162,6 +1163,7 @@ def generate_configdrive(session, instance, vm_ref, userdevice,
                     utils.execute('dd',
                                   'if=%s' % tmp_file,
                                   'of=%s' % dev_path,
+                                  'bs=%d' % DD_BLOCKSIZE,
                                   'oflag=direct,sync',
                                   run_as_root=True)
 
@@ -2429,6 +2431,7 @@ def _copy_partition(session, src_ref, dst_ref, partition, virtual_size):
                 utils.execute('dd',
                               'if=%s' % src_path,
                               'of=%s' % dst_path,
+                              'bs=%d' % DD_BLOCKSIZE,
                               'count=%d' % num_blocks,
                               'iflag=direct,sync',
                               'oflag=direct,sync',