yahoo-eng-team team mailing list archive

[Dan Smith <dms@xxxxxxxxxxxxx>]

Public bug reported:

Nova does not currently support multiple rbd backends. However, Glance
does and an operator may point Nova at a Glance with access to multiple
RBD clusters. If this happens, Nova will silently download the image
from Glance, flatten it, and upload it to the local RBD cluster named
privately to the image. If another instance is booted from the same
image, this will happen again, using more network resources and
duplicating the image on ceph for the second and subsequent instances.
When configuring Nova and Glance for shared RBD, the expectation is that
instances are fast-cloned from Glance base images, so this silent
behavior of using a lot of storage would be highly undesirable and
unexpected. Since operators control the backend config, but users upload
images (and currently only to one backend), it is the users that would
trigger this additional consumption of storage.

This isn't really a bug in Nova per se, since Nova does not claim to
support multiple backends and is download/uploading the image in the
same way it would if the image was located on any other not-the-same-as-
my-RBD-cluster location. It is, however, unexpected and undesirable
behavior.

** Affects: nova
     Importance: Undecided
         Status: New

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https://bugs.launchpad.net/bugs/1858877

Title:
  Silent wasted storage with multiple RBD backends

Status in OpenStack Compute (nova):
  New

Bug description:
  Nova does not currently support multiple rbd backends. However, Glance
  does and an operator may point Nova at a Glance with access to
  multiple RBD clusters. If this happens, Nova will silently download
  the image from Glance, flatten it, and upload it to the local RBD
  cluster named privately to the image. If another instance is booted
  from the same image, this will happen again, using more network
  resources and duplicating the image on ceph for the second and
  subsequent instances. When configuring Nova and Glance for shared RBD,
  the expectation is that instances are fast-cloned from Glance base
  images, so this silent behavior of using a lot of storage would be
  highly undesirable and unexpected. Since operators control the backend
  config, but users upload images (and currently only to one backend),
  it is the users that would trigger this additional consumption of
  storage.

  This isn't really a bug in Nova per se, since Nova does not claim to
  support multiple backends and is download/uploading the image in the
  same way it would if the image was located on any other not-the-same-
  as-my-RBD-cluster location. It is, however, unexpected and undesirable
  behavior.

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