diff --git a/nova/block_device.py b/nova/block_device.py
index c0113a350ad1..89c203b1d774 100644
--- a/nova/block_device.py
+++ b/nova/block_device.py
@@ -509,6 +509,32 @@ def get_device_letter(device_name):
     return _nums.sub('', letter) if device_name else device_name
 
 
+def generate_device_letter(index):
+    """Returns device letter by index (starts by zero)
+       i.e.
+       index   = 0, 1,..., 18277
+       results = a, b,..., zzz
+    """
+    base = ord('z') - ord('a') + 1
+    unit_dev_name = ""
+    while index >= 0:
+        letter = chr(ord('a') + (index % base))
+        unit_dev_name = letter + unit_dev_name
+        index = int(index / base) - 1
+
+    return unit_dev_name
+
+
+def generate_device_name(prefix, index):
+    """Returns device unit name by index (starts by zero)
+       i.e.
+       prefix  = vd
+       index   = 0, 1,..., 18277
+       results = vda, vdb,..., vdzzz
+    """
+    return prefix + generate_device_letter(index)
+
+
 def instance_block_mapping(instance, bdms):
     root_device_name = instance['root_device_name']
     # NOTE(clayg): remove this when xenapi is setting default_root_device
diff --git a/nova/tests/unit/test_block_device.py b/nova/tests/unit/test_block_device.py
index 52939cd3dd73..abf265818a32 100644
--- a/nova/tests/unit/test_block_device.py
+++ b/nova/tests/unit/test_block_device.py
@@ -149,6 +149,20 @@ class BlockDeviceTestCase(test.NoDBTestCase):
         self.assertEqual('c', block_device.get_device_letter('hdc'))
         self.assertIsNone(block_device.get_device_letter(None))
 
+    def test_generate_device_name(self):
+        expected = (
+                ('vda', ("vd", 0)),
+                ('vdaa', ("vd", 26)),
+                ('vdabc', ("vd", 730)),
+                ('vdidpok', ("vd", 4194304)),
+                ('sdc', ("sd", 2)),
+                ('sdaa', ("sd", 26)),
+                ('sdiw', ("sd", 256)),
+                ('hdzz', ("hd", 701))
+                )
+        for res, args in expected:
+            self.assertEqual(res, block_device.generate_device_name(*args))
+
     def test_volume_in_mapping(self):
         swap = {'device_name': '/dev/sdb',
                 'swap_size': 1}