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Cinder

Cinder: The Block Storage Service in OpenStack

Cinder is the OpenStack service that provides persistent block storage to running instances. It allows users to create, attach, and manage volumes, which can be used as additional storage for virtual machines (VMs) or as bootable disks.

How Cinder Works

Cinder operates through several key components and processes:

  1. cinder-api: The API server that handles requests for creating, attaching, and managing volumes. It exposes a RESTful API for interacting with the block storage service.
  2. cinder-scheduler: Determines the optimal storage provider node to create a volume based on resource availability and policies.
  3. cinder-volume: Manages the lifecycle of volumes, including creation, deletion, and attachment to instances. It interacts with the storage backend to perform these operations.
  4. cinder-backup: Provides backup services for volumes, allowing users to back up their data to an external storage system, such as OpenStack Swift.
  5. Database: Stores metadata about volumes, such as their size, status, and location.
  6. Message Queue: Facilitates communication between the various Cinder components.

Practical Analogy

Think of Cinder as a library of external hard drives:

  • cinder-api: The library’s front desk where users request to borrow or return hard drives (volumes).
  • cinder-scheduler: The librarian who decides which shelf (storage provider) to place a new hard drive on, based on available space and other criteria.
  • cinder-volume: The library staff who manage the hard drives, ensuring they are properly stored, retrieved, and attached to users’ computers (instances).
  • cinder-backup: The backup service that allows users to make copies of their hard drives and store them in a safe place.
  • Database: The library’s catalog that keeps track of all the hard drives, their details, and their current status.
  • Message Queue: The internal communication system used by the library staff to coordinate their tasks.

Practical Use-Cases

  1. Persistent Storage for VMs: Cinder provides persistent storage that can be attached to VMs, ensuring that data is retained even if the VM is terminated.
  2. Bootable Volumes: Users can create bootable volumes from images stored in Glance and use them to launch instances, providing a flexible way to manage operating system images.
  3. Database Storage: Databases often require high-performance, reliable storage. Cinder volumes can be used to store database files, ensuring data integrity and performance.
  4. Backup and Recovery: Cinder’s backup service allows users to create backups of their volumes, providing a way to recover data in case of failures or data loss.
  5. Data Migration: Users can detach volumes from one instance and attach them to another, facilitating data migration and workload mobility within the cloud environment.

Cinder’s ability to provide scalable, reliable block storage makes it an essential component of the OpenStack ecosystem, supporting a wide range of applications and use cases.

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