Track cinder capacity notifications

The goal of this blueprint is to capture the capacity notifications emitted by cinder service when it notifies storage capacity information to ceilometer.

Problem description

Cinder service collects storage capacity information about each pool/backend. These includes total/free/allocated/provisioned/virtual_free capacity info. Cinder service emits the formatted information as notifications periodically.

It’s better for ceilometer service to add a notification plugin to listen to the topic. If the information payload can be consumed and transformed into samples, it will be helpful for admin users to have an estimation of the future capacity planning.

Proposed change

Add new metrics for different capacity information carried by capacity payload from notifications emitted by Cinder. They will include:

  • CapacityTotalSize It is the total physical capacity of a pool/backend.

  • CapacityFreeSize It is the real physical available capacity of a pool/backend.

  • CapacityAllocatedSize It is the physical capacity allocated directly thru Cinder. Note: The capacity which is not allocated thru Cinder is not included in.

  • CapacityProvisionedSize It is the capacity which has been provisioned in a pool/backend.

    Note: It includes the capacity both allocated directly thru Cinder and not. The provisioned capacity size is equal or greater than the allocated size.

  • CapacityVirtualfreeSize It is the apparent available virtual capacity means how much capacity can still provision besides the capacity which has been provisioned already in the pool/backend.

    Note: It is different from free capacity, free capacity is related to real available physical capacity. For thin provisioning support, due to the max_over_subscription_ratio, the provisioned capacity can be much larger than the real physical capacity.

    Please reference to get the detail explanation of above terminology.

Each metric extracts the capacity information which it is interested in from the notification payload. The admin users can utilize ceilometer statistics API to get the sum of each kind of capacity. Also they can utilize the horizon resource usage page to get the chart of the trend of each kind of capacity information.



Data model impact


REST API impact


Security impact


Pipeline impact


Other end user impact


Performance/Scalability Impacts

No new impacts. Pre-existing concerns with capacity at the notification and storage handling layers remain.

Other deployer impact


Developer impact




Primary assignee:


Ongoing maintainer:


Work Items

  • Add metric

  • Add metric

  • Add capacity.allocated.size metric

  • Add capacity.provisioned.size metric

  • Add capacity.virtual_free.size metric

  • Test coverage for the above metrics and samples validation.

Future lifecycle

In the future new types of capacity notifications maybe expected from the Cinder service to account for the statistics data. These will need to be handled later.




Unit and integration Tests will be added to cover the necessary metrics and validate samples generated.

Documentation Impact

The added metrics will need to be documented in the measurements section.