[ceph] instance snapshot

asked 2017-04-18 13:58:59 -0600

Damian Dąbrowski gravatar image


Im wondering about snapshotting instances using ceph rbd backend.

For example: If I have instance based on root disk I can easily snapshot it, but it actually is copy-on-write clone of a block device snapshot. Snapshots are flattened - cloned images doesn't retain a reference to the parent snapshot.

Is there any way to make openstack snapshot of VM which depends on parent image? I don't want to clone snapshot and make independent image. I just want to make quick snapshot. Nothing more.

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An instance snapshot uploads an image to the Glance store; it's never a copy-on-write AFAIK. But perhaps I don't understand you. Where is RBD in your setup - is it the Glance store, the backend for ephemeral storage, or both?

Bernd Bausch gravatar imageBernd Bausch ( 2017-04-19 00:58:56 -0600 )edit

I agree with Bernd Bausch, the question is not really clear. There are nova snapshots (create a new glance image --> flattened), and there are rbd snapshots (cow-clone), we use them for backups to keep instances running while rbd flattens and exports the images.

eblock gravatar imageeblock ( 2017-04-19 05:12:51 -0600 )edit

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answered 2018-07-05 08:03:21 -0600

paubry gravatar image

I guess this spec is what you want:

https://specs.openstack.org/openstack/nova-specs/specs/mitaka/implemented/rbd-instance-snapshots.html (https://specs.openstack.org/openstack...)

Sebatian HAN has a nice post on this: http://www.sebastien-han.fr/blog/2015/10/05/openstack-nova-snapshots-on-ceph-rbd/ (http://www.sebastien-han.fr/blog/2015...)

As far as I can see, this is merged upstream since the Mitaka release:


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answered 2017-04-19 08:41:07 -0600

Damian Dąbrowski gravatar image


Thanks for the answers.

@Bernd - I use ceph as backend for block, ephemeral and image storage and You were right, glance images aren't copy-on-write, sorry for my bad.

@eblock I'm talking about nova snapshots. As You said they are flattened. But I want to create COW-clone of openstack instance(will be excellent if I could do this from horizon).

I hope You can understand me now. Is there any way to do this?

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Correct me if I'm wrong, I believe this is only possible in the rbd layer. IIUC, you would like the rbd snap create command to be the functionality behind the nova snapshot button, so that you would decide individually for every snapshot what its purpose is? I guess that's not the OpenStack design

eblock gravatar imageeblock ( 2017-04-20 03:50:12 -0600 )edit

Ok, I think you are right, it's only possible in rbd layer. Thank You eblock.

Damian Dąbrowski gravatar imageDamian Dąbrowski ( 2017-04-20 04:05:39 -0600 )edit

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Asked: 2017-04-18 13:58:59 -0600

Seen: 1,115 times

Last updated: Apr 19 '17