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cinder consumption

asked 2013-08-14 07:05:26 -0500

djangoat gravatar image

updated 2013-08-14 19:47:51 -0500

sgordon gravatar image

I would like to ask two questions regarding cinder:

Question 1: For example I have created a cinder-volume group with 500gb Does it mean this mean the maximum size of volumes that are able to be created by a user or this is the actual volume size allocated for volume creation. ( for example there is a 5 volumes created by users with 100GB each, the next user who wants to create a new volume are not able to do it because the 500gb allotted volume for cinder is already been consumed)

Question 2: Where does the cinder volume consume disk space, is it on the controller node or in the compute node?

Thanks a lot

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answered 2013-08-14 19:45:57 -0500

sgordon gravatar image

updated 2013-08-15 08:41:38 -0500

Question 1

For example I have created a cinder-volume group with 500gb Does it mean this is the maximum size of volume that are able to be created by a user or this is the actual volume size allotted for volume creation.

When using LVM as the storage backend the size of the volume group(s) (by default cinder-volumes) determines the total size allocated for volume storage. In your example where cinder-volumes is 500 GB in size:

  • If 5 volumes are created by different users (or the same user) with a size of 100 GB each then no space is left for new volumes.
  • If 1 volume is created by a user with a size of 500 GB then no space is left for new volumes.

Applying restrictions to how much volume storage each user or tenant can use is handled separately using quotas.

Question 2

Where do the cinder volume consumed disk space, Is it in the controller node or in the compute node?

The space is consumed on the node that hosts the volume group. In a setup with one controller node servicing multiple compute nodes this will typically be the controller. There is however nothing stopping the use of multiple instances of the cinder-volumes service on separate storage nodes (or even on a single storage node), each with their own backend storage.

Note that compute nodes must still have some storage available for the software itself, logs, and ephemeral storage. See for more information on ephermeral storage and the difference between it versus volume storage.

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thanks a lot, very informative

djangoat gravatar imagedjangoat ( 2013-08-15 21:41:44 -0500 )edit

So it means , I need to have a much larger storage device in controller node. Is it possible to create the cinder volume group from other partition in my disk drive. for example I have 4TB Disk Drive and I have partition it into 2. Disk 1: 200gb Disk2: 3.6TB Is it possible to point the cinder volume creation into Disk2 Thanks

djangoat gravatar imagedjangoat ( 2013-08-15 21:48:17 -0500 )edit

Yes, you can use the standard LVM tools (pvcreate, vgcreate, etc.) to create the volume group on any drive or partition that you choose to. To tell cinder which volume group to use update the volume_group key in /etc/cinder/cinder.conf to the name of the new volume group.

sgordon gravatar imagesgordon ( 2013-08-15 21:54:59 -0500 )edit

answered 2013-08-15 00:10:50 -0500

jgriffith gravatar image

Actually, you're statement was correct, and so was the reponse added by the user above. There are two things that control the amount of block-storage that a tenant/user can deploy.

The first is as you guessed, the available space in the cinder-volume VG. If you're not using thin provisioning then the 500Gb capacity of the VG is in fact all you have for both Volumes and Snapshots. In addition, as the other poster pointed out there are also quotas assigned to each user. This included GB's of volumes and snapshots allowed as well as total number of volumes and snapshots allowed. There are additional quotas as well but those two are the primary ones regarding your question.

As far as where the VG cinder-volumes is located. It's not actually on the controller, it's on what's called a Cinder volume node. The machine/node that is running the cinder volume-service. You can add cinder-volume nodes/services to grow and scale over time. You can also have multiple cinder volume services running on a single machine that points to different VG's or external SAN based storage.

Hope that helps.

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thanks a lot for answering.

djangoat gravatar imagedjangoat ( 2013-08-15 21:42:19 -0500 )edit

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Asked: 2013-08-14 07:05:26 -0500

Seen: 1,695 times

Last updated: Aug 15 '13