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[Bug 1177927] Re: VHD snapshot from Hyper-V driver is bigger than original instance

To: yahoo-eng-team@xxxxxxxxxxxxxxxxxxx
From: Thierry Carrez <thierry.carrez+lp@xxxxxxxxx>
Date: Thu, 03 Oct 2013 07:58:51 -0000
Reply-to: Bug 1177927 <1177927@xxxxxxxxxxxxxxxxxx>
Sender: bounces@xxxxxxxxxxxxx
** Changed in: nova
       Status: Fix Committed => Fix Released

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https://bugs.launchpad.net/bugs/1177927

Title:
  VHD snapshot from Hyper-V driver is bigger than original instance

Status in OpenStack Compute (Nova):
  Fix Released

Bug description:
  This is discussed a bit in bug 1177820.  This is on stable/grizzly
  where the compute node is running the hyper-v driver.

  The user has this RHEL 6.4 x86_64 instance:

  IBM-SCE> nova show 83604044-a5e0-44ff-b214-d1a91d0ec244
  +-------------------------------------+-------------------------------------------------------------+
  | Property                            | Value                                                       |
  +-------------------------------------+-------------------------------------------------------------+
  | status                              | SHUTOFF                                                     |
  | updated                             | 2013-05-08T07:17:53Z                                        |
  | OS-EXT-STS:task_state               | None                                                        |
  | OS-EXT-SRV-ATTR:host                | abba-n04-hv01                                               |
  | key_name                            | None                                                        |
  | image                               | RHEL64-Server-x86_64 (f526d15d-5ab8-4217-a450-a1ccb78d984d) |
  | VLAN_160 network                    | 10.160.0.11                                                 |
  | hostId                              | 169746d480604c1349d8c0c0a4ba866211f3f00a2eebf30c87b7390d    |
  | OS-EXT-STS:vm_state                 | stopped                                                     |
  | OS-EXT-SRV-ATTR:instance_name       | instance-0000003d                                           |
  | OS-EXT-SRV-ATTR:hypervisor_hostname | abba-n04-hv01                                               |
  | flavor                              | m1.small (2)                                                |
  | id                                  | 83604044-a5e0-44ff-b214-d1a91d0ec244                        |
  | security_groups                     | [{u'name': u'default'}]                                     |
  | user_id                             | 8e4c4785db6245e7add265e6cf62c67f                            |
  | name                                | RHELBR-1                                                    |
  | created                             | 2013-05-08T06:56:52Z                                        |
  | tenant_id                           | 6f858c1594b8461cb7000829e3977e9d                            |
  | OS-DCF:diskConfig                   | MANUAL                                                      |
  | metadata                            | {}                                                          |
  | accessIPv4                          |                                                             |
  | accessIPv6                          |                                                             |
  | OS-EXT-STS:power_state              | 4                                                           |
  | OS-EXT-AZ:availability_zone         | nova                                                        |
  | config_drive                        | true                                                        |
  +-------------------------------------+-------------------------------------------------------------+

  
  With this flavor:

  IBM-SCE> nova flavor-show m1.small
  +----------------------------+----------+
  | Property                   | Value    |
  +----------------------------+----------+
  | name                       | m1.small |
  | ram                        | 2048     |
  | OS-FLV-DISABLED:disabled   | False    |
  | vcpus                      | 1        |
  | extra_specs                | {}       |
  | swap                       |          |
  | os-flavor-access:is_public | True     |
  | rxtx_factor                | 1.0      |
  | OS-FLV-EXT-DATA:ephemeral  | 0        |
  | disk                       | 20       |
  | id                         | 2        |
  +----------------------------+----------+

  They create a snapshot image of that instance and try to boot an
  instance from the snapshot but it fails with an ImageTooLarge error.
  It turns out that the snapshot image is slightly bigger than the
  original instance.  This is the snapshot image details:

  Id: 71410397-ba95-4a44-92cd-e62b3bbe1a14
  Public: No
  Protected: No
  Name: RHELBR-B1_backup
  Status: active
  Size: 21474836992
  Disk format: vhd
  Container format: bare
  Minimum Ram Required (MB): 0
  Minimum Disk Required (GB): 0
  Owner: 6f858c1594b8461cb7000829e3977e9d

  When converting that size to GB, it comes to 20.000000477 GB.  I'm not
  sure if they should be using a raw or qcow2 disk format, but it still
  seems like a problem that the snapshot is reported as bigger than the
  original instance.

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