4.2. Consumers of Block Storage QoS specifications
When you create a QoS specification you must choose the required consumer. The consumer determines where you want to apply the QoS limits and determines which QoS property keys are available to define the QoS limits.
The Block Storage service (cinder) supports the following consumers of QoS specifications:
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front-end: The Compute service (nova) applies the QoS limits when the volume is attached to an instance. The Compute service supports all the QoS property keys provided by the Block Storage service. back-end: The back-end driver of the associated volume type applies the QoS limits. Each back-end driver supports their own set of QoS property keys. For more information on which QoS property keys the driver supports, see the back-end driver documentation.You would use the
back-endconsumer in cases where thefront-endconsumer is not supported. For example, when attaching volumes to bare-metal nodes through the Bare Metal Provisioning service (ironic).both: Both consumers apply the QoS limits, where possible. This consumer type therefore supports the following QoS property keys:- When a volume is attached to an instance, then you can use every QoS property key that both the Compute service and the back-end driver supports.
- When the volume is not attached to an instance, then you can only use the QoS property keys that the back-end driver supports.
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