“cinder-scheduler” service

The Cinder scheduler is an essential component of the Cinder service. Its primary function is to determine the optimal storage backends to fulfill volume creation requests based on various criteria, such as availability, capacity, performance, and configured policies.

When a user requests the creation of a volume, the request is sent to the Cinder API service. The API service then forwards the request to the Cinder scheduler. The scheduler analyzes the request and selects the most appropriate storage backend(s) to allocate the volume.

Here’s an overview of how the Cinder scheduler works:

  1. Resource Discovery: The scheduler collects information about the available storage backends by communicating with the Cinder volume service. The volume service regularly updates the scheduler with the status and capabilities of each backend.
  2. Filtering: The scheduler applies filters to the available storage backends based on criteria specified in the volume request. Filters can include attributes like availability zone, volume type, backend capabilities, and more. The goal is to narrow down the list of potential backends that can fulfill the request.
  3. Weighing: After the filtering process, the scheduler assigns weights to the remaining backends based on configurable policies. Weights indicate the suitability of each backend for fulfilling the request. The policies can consider factors like backend capacity, utilization, performance, proximity, and other user-defined criteria.
  4. Backend Selection: The scheduler selects one or more backends with the highest weights and returns them to the Cinder API service. The API service then instructs the volume service to create the volume on the chosen backend(s).
  5. Rescheduling: If the selected backend fails to create the volume for any reason (e.g., insufficient capacity), the scheduler can be configured to retry the selection process with a different set of available backends.

The Cinder scheduler’s flexibility allows operators to configure and customize its behavior according to their specific requirements. They can define filters, weighting algorithms, and policies to influence the selection process and ensure the optimal utilization of storage resources.

Additionally, the Cinder scheduler supports advanced features like multi-backend scheduling, where a single volume request can be split across multiple storage backends to achieve features like data replication or tiered storage.

In summary, the Cinder scheduler plays a crucial role in the OpenStack Cinder service by efficiently selecting the most suitable storage backends based on configurable policies and constraints. Its intelligent decision-making helps optimize storage resource utilization and improve overall performance in an OpenStack deployment.

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