Cannot add more than 25 volumes to an instance in openstack.

Issue

• Getting HTTP5XX exceeded error whenever the user tries to attach more than 25 volumes to an instance.

  2018-05-29 13:49:41.076 14480 ERROR nova.api.openstack.extensions [req-4d22806c-f75f-4a16-8635-33aba2c7831b 245a7e95b00d476a83c21ec789873473 9003565472dc48b28826c53f3888f5aa - default default] Unexpected exception in API method
  2018-05-29 13:49:41.076 14480 ERROR nova.api.openstack.extensions Traceback (most recent call last):
  2018-05-29 13:49:41.076 14480 ERROR nova.api.openstack.extensions   File "/usr/lib/python2.7/site-packages/nova/api/openstack/extensions.py", line 338, in wrapped
  2018-05-29 13:49:41.076 14480 ERROR nova.api.openstack.extensions     return f(*args, **kwargs)
  2018-05-29 13:49:41.076 14480 ERROR nova.api.openstack.extensions   File "/usr/lib/python2.7/site-packages/nova/api/validation/__init__.py", line 73, in wrapper
  2018-05-29 13:49:41.076 14480 ERROR nova.api.openstack.extensions     return func(*args, **kwargs)
  2018-05-29 13:49:41.076 14480 ERROR nova.api.openstack.extensions   File "/usr/lib/python2.7/site-packages/nova/api/openstack/compute/volumes.py", line 325, in create
  2018-05-29 13:49:41.076 14480 ERROR nova.api.openstack.extensions     volume_id, device)
  2018-05-29 13:49:41.076 14480 ERROR nova.api.openstack.extensions   File "/usr/lib/python2.7/site-packages/nova/compute/api.py", line 166, in inner
  2018-05-29 13:49:41.076 14480 ERROR nova.api.openstack.extensions     return function(self, context, instance, *args, **kwargs)
  2018-05-29 13:49:41.076 14480 ERROR nova.api.openstack.extensions   File "/usr/lib/python2.7/site-packages/nova/compute/api.py", line 147, in inner
  2018-05-29 13:49:41.076 14480 ERROR nova.api.openstack.extensions     return f(self, context, instance, *args, **kw)
  2018-05-29 13:49:41.076 14480 ERROR nova.api.openstack.extensions   File "/usr/lib/python2.7/site-packages/nova/compute/api.py", line 3521, in attach_volume
  2018-05-29 13:49:41.076 14480 ERROR nova.api.openstack.extensions     disk_bus, device_type)
  2018-05-29 13:49:41.076 14480 ERROR nova.api.openstack.extensions   File "/usr/lib/python2.7/site-packages/nova/compute/api.py", line 3458, in _attach_volume
  2018-05-29 13:49:41.076 14480 ERROR nova.api.openstack.extensions     device_type=device_type)
  2018-05-29 13:49:41.076 14480 ERROR nova.api.openstack.extensions   File "/usr/lib/python2.7/site-packages/nova/compute/api.py", line 3440, in _create_volume_bdm
  2018-05-29 13:49:41.076 14480 ERROR nova.api.openstack.extensions     device_type=device_type)
  2018-05-29 13:49:41.076 14480 ERROR nova.api.openstack.extensions   File "/usr/lib/python2.7/site-packages/nova/compute/rpcapi.py", line 926, in reserve_block_device_name
  2018-05-29 13:49:41.076 14480 ERROR nova.api.openstack.extensions     return cctxt.call(ctxt, 'reserve_block_device_name', **kw)
  2018-05-29 13:49:41.076 14480 ERROR nova.api.openstack.extensions   File "/usr/lib/python2.7/site-packages/oslo_messaging/rpc/client.py", line 169, in call
  2018-05-29 13:49:41.076 14480 ERROR nova.api.openstack.extensions     retry=self.retry)
  2018-05-29 13:49:41.076 14480 ERROR nova.api.openstack.extensions   File "/usr/lib/python2.7/site-packages/oslo_messaging/transport.py", line 97, in _send
  2018-05-29 13:49:41.076 14480 ERROR nova.api.openstack.extensions     timeout=timeout, retry=retry)
  2018-05-29 13:49:41.076 14480 ERROR nova.api.openstack.extensions   File "/usr/lib/python2.7/site-packages/oslo_messaging/_drivers/amqpdriver.py", line 584, in send
  2018-05-29 13:49:41.076 14480 ERROR nova.api.openstack.extensions     retry=retry)
  2018-05-29 13:49:41.076 14480 ERROR nova.api.openstack.extensions   File "/usr/lib/python2.7/site-packages/oslo_messaging/_drivers/amqpdriver.py", line 575, in _send
  2018-05-29 13:49:41.076 14480 ERROR nova.api.openstack.extensions     raise result
  2018-05-29 13:49:41.076 14480 ERROR nova.api.openstack.extensions NovaException_Remote: No free disk device names for prefix 'sd'