[Bug 1327021] [NEW] regression in snapshot performance in trusty

[Michael Hudson-Doyle]

Public bug reported:

'nova image-create' is a lot slower on a trusty openstack than a precise
one:

+---------+--------+----------------+-------------------+
| ubuntu  | image  | disk size (GB) | snapshot time (s) |
+---------+--------+----------------+-------------------+
| precise | cirros | 1              | 6                 |
+---------+--------+----------------+-------------------+
| precise | cirros | 10             | 6                 |
+---------+--------+----------------+-------------------+
| precise | trusty | 10             | 38                |
+---------+--------+----------------+-------------------+
| trusty  | cirros | 1              | 15                |
+---------+--------+----------------+-------------------+
| trusty  | cirros | 10             | 61                |
+---------+--------+----------------+-------------------+
| trusty  | trusty | 10             | 100               |
+---------+--------+----------------+-------------------+

It's also interesting that the time in trusty appears to depend on the
disk size whereas it didn't in trusty.  AFAICT the nova code is the same
in both havana and icehouse, leaving libvirt as the most likely culprit
-- but this is not confirmed.

** Affects: libvirt (Ubuntu)
     Importance: Undecided
         Status: New

** Description changed:

  'nova image-create' is a lot slower on a trusty openstack than a precise
  one:
  
  +---------+--------+----------------+-------------------+
- | ubuntu  | image  | disk size (GB) | snapshot time (s) |
+ | ubuntu  | image  | disk size (GB) | snapshot time (s) |
  +---------+--------+----------------+-------------------+
- | precise | cirros | 1              | 6                 |
+ | precise | cirros | 1              | 6                 |
  +---------+--------+----------------+-------------------+
- | precise | cirros | 10             | 6                 |
+ | precise | cirros | 10             | 6                 |
  +---------+--------+----------------+-------------------+
- | precise | trusty | 10             | 38                |
+ | precise | trusty | 10             | 38                |
  +---------+--------+----------------+-------------------+
- | trusty  | cirros | 1              | 15                |
+ | trusty  | cirros | 1              | 15                |
  +---------+--------+----------------+-------------------+
- | trusty  | cirros | 10             | 61                |
+ | trusty  | cirros | 10             | 61                |
  +---------+--------+----------------+-------------------+
- | trusty  | trusty | 10             | 100               |
+ | trusty  | trusty | 10             | 100               |
  +---------+--------+----------------+-------------------+
  
  It's also interesting that the time in trusty appears to depend on the
  disk size whereas it didn't in trusty.  AFAICT the nova code is the same
  in both havana and icehouse, leaving libvirt as the most likely culprit
  -- but this is not confirmed.

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https://bugs.launchpad.net/bugs/1327021

Title:
  regression in snapshot performance in trusty

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