Open Stack

Hi all,

I used a heat template to launch a server and attach cinder volume to it.
I found that if I use the block_device_mapping parameter in my server 
properties, then it will took a very long time to detach the volume when 
I delete the stack; without block_device_mapping, the volume will be 
immediately detached.

And I don't see any difference from the VM's perspective, whether I use 
block_device_mapping or not, the volume will be attached the my VM as 'vdb'.

I am curious about what does this block_device_mapping mean and what 
difference does nova behave under the hood.

Here's my heat template:

heat_template_version: 2013-05-23

description: |
   jfdkfjdk System
outputs:
   instance_ip:
     description: the ip address
     value: {get_attr: [Myserver, networks, OAM120, 0]}
parameters:
   image_name:
     label: Image
     type: string
     default: MCcloudinit

   flavor_name:
     label: fff
     type: string
     default: 4x8x160
   prinet1:
     label: Netffd
     type: string
     default: OAM120
resources:
   Myserver:
     metadata:
       mytest_id: tzhou002isgreat
     type: OS::Nova::Server
     properties:
       availability_zone: nova
       block_device_mapping: [
         {volume_id: {get_resource: disk1},
         delete_on_termination: 'true',
         device_name: vdb}]
       flavor: { get_param: flavor_name }
       image: { get_param: image_name }
       config_drive: 'True'
       name:
         str_replace:
           params:
             $system_name: {get_param: "OS::stack_name"}
           template: $system_name-0-0-1
       networks:
       - network: {get_param: prinet1}
       security_groups: [default]
   disk1:
     type: OS::Cinder::Volume
     properties:
       availability_zone: nova
       name: server1_disk1
       size: '1'
   disk_attach:
     type: OS::Cinder::VolumeAttachment
     properties:
       instance_uuid: {get_resource: Myserver}
       volume_id: {get_resource: disk1}

   mymultipartmime:
     properties:
       parts:
       - config: {get_resource: 'Myserver'}
       - config: {get_resource: 'disk1'}
     type: OS::Heat::MultipartMime