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      Licensed under the Apache License, Version 2.0 (the "License"); you may
      not use this file except in compliance with the License. You may obtain
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          http://www.apache.org/licenses/LICENSE-2.0

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      under the License.

Drivers
=======

Cinder exposes an API to users to interact with different storage backend
solutions. The following are standards across all drivers for Cinder services
to properly interact with a driver.

Minimum Features
----------------

Minimum features are enforced to avoid having a grid of what features are
supported by which drivers and which releases. Cinder Core requires that all
drivers implement the following minimum features.

Core Functionality
------------------

* Volume Create/Delete
* Volume Attach/Detach
* Snapshot Create/Delete
* Create Volume from Snapshot
* Get Volume Stats
* Copy Image to Volume
* Copy Volume to Image
* Clone Volume
* Extend Volume

Volume Stats
------------

Volume stats are used by the different schedulers for the drivers to provide
a report on their current state of the backend. The following should be
provided by a driver.

* driver_version
* free_capacity_gb
* reserved_percentage
* storage_protocol
* total_capacity_gb
* vendor_name
* volume_backend_name

**NOTE:** If the driver is unable to provide a value for free_capacity_gb or
total_capacity_gb, keywords can be provided instead. Please use 'unknown' if
the array cannot report the value or 'infinite' if the array has no upper
limit.

Feature Enforcement
-------------------

All concrete driver implementations should use the
``cinder.interface.volumedriver`` decorator on the driver class::

    @interface.volumedriver
    class LVMVolumeDriver(driver.VolumeDriver):

This will register the driver and allow automated compliance tests to run
against and verify the compliance of the driver against the required interface
to support the `Core Functionality`_ listed above.

Running ``tox -e compliance`` will verify all registered drivers comply to
this interface. This can be used during development to perform self checks
along the way. Any missing method calls will be identified by the compliance
tests.

The details for the required volume driver interfaces can be found in the
``cinder/interface/volume_*_driver.py`` source.