Sean McGinnis 3c18c6f440 Add interface documentation to driver devref

Link the docstring generated documentation for the driver interfaces into
the drivers devref page for easy access to driver method documentation.

Change-Id: Ie22599fef99ebfac12f3b9bb251ae5bdfff4bff6

2016-07-24 17:23:29 -05:00

4.7 KiB

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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.

Driver Development Documentations

The LVM driver is our reference for all new driver implementations. The information below can provide additional documentation for the methods that volume drivers need to implement.

Base Driver Interface

The methods documented below are the minimum required interface for a volume driver to support. All methods from this interface must be implemented in order to be an official Cinder volume driver.

cinder.interface.volume_driver

Snapshot Interface

Another required interface for a volume driver to be fully compatible is the ability to create and manage snapshots. Due to legacy constraints, this interface is not included in the base driver interface above.

Work is being done to address those legacy issues. Once that is complete, this interface will be merged with the base driver interface.

cinder.interface.volume_snapshot_driver

Manage/Unmanage Support

An optional feature a volume backend can support is the ability to manage existing volumes or unmanage volumes - keep the volume on the storage backend but no longer manage it through Cinder.

To support this functionality, volume drivers must implement these methods:

cinder.interface.volume_management_driver

Manage/Unmanage Snapshot Support

In addition to the ability to manage and unmanage volumes, Cinder backend drivers may also support managing and unmanaging volume snapshots. These additional methods must be implemented to support these operations.

cinder.interface.volume_snapshotmanagement_driver

Volume Consistency Groups

Some storage backends support the ability to group volumes and create write consistent snapshots across the group. In order to support these operations, the following interface must be implemented by the driver.

cinder.interface.volume_consistencygroup_driver

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