cinder.interface.volume_driver module

Core backend volume driver interface.

All backend drivers should support this interface as a bare minimum, but some methods (marked as optional in their description) can rely on the default implementation.

class VolumeDriverCore

Bases: CinderInterface

Core backend driver required interface.


Validate there are no issues with the driver configuration.

Called after do_setup(). Driver initialization can occur there or in this call, but must be complete by the time this returns.

If this method raises an exception, the driver will be left in an “uninitialized” state by the volume manager, which means that it will not be sent requests for volume operations.

This method typically checks things like whether the configured credentials can be used to log in the storage backend, and whether any external dependencies are present and working.


VolumeBackendAPIException – in case of setup error.

clone_image(context, volume, image_location, image_meta, image_service)

Create a volume efficiently from an existing image.

Drivers that, always or under some circumstances, can efficiently create a volume from a Glance image can implement this method to be given a chance to try to do the volume creation as efficiently as possible.

If the driver cannot do it efficiently on a specific call it can return (None, False) to let Cinder try other mechanisms.

This method is optional and most drivers won’t need to implement it and can leverage the default driver implementation that returns (None, False) to indicate that this optimization is not possible on this driver.

Examples where drivers can do this optimization:

  • When images are stored on the same storage system and the driver can locate them and efficiently create a volume. For example the RBD driver can efficiently create a volume if the image is stored on the same Ceph cluster and the image format is raw. Another example is the GPFS driver.

  • When volumes are locally accessible and accessing them that way is more efficient than going through the remote connection mechanism. For example in the GPFS driver if the cloning feature doesn’t work it will copy the file without using os-brick to connect to the volume.

  • context – Security/policy info for the request.

  • volume – The volume to create, as an OVO instance. Drivers should use attributes to access its values instead of using the dictionary compatibility interface it provides.

  • image_location – Tuple with (direct_url, locations) from the image metadata fields. direct_url, when present, is a string whose format depends on the image service’s external storage in use. Any, or both, tuple positions can be None, depending on the image service configuration. locations, when present, is a list of dictionaries where the value of the url key contains the direct urls (including the one from direct_url).

  • image_meta – Dictionary containing information about the image, including basic attributes and custom properties. Some transformations have been applied, such as converting timestamps (from created_at, updated_at, and deleted_at) to datetimes, and deserializing JSON values from block_device_mapping and mappings keys if present. Base properties, as per the image’s schema, will be stored on the base dictionary and the rest will be stored under the properties key. An important field to check in this method is the disk_format (e.g. raw, qcow2).

  • image_service – The image service to use (GlanceImageService instance). Can fetch image data directly using it.


Tuple of (model_update, boolean) where the boolean specifies whether the clone occurred.

copy_image_to_volume(context, volume, image_service, image_id, disable_sparse=False)

Fetch the image from image_service and write it to the volume.

  • context – Security/policy info for the request.

  • volume – The volume to create.

  • image_service – The image service to use.

  • image_id – The image identifier.

  • disable_sparse – Enable or disable sparse copy. Default=False.


Model updates.

copy_volume_to_image(context, volume, image_service, image_meta)

Copy the volume to the specified image.

  • context – Security/policy info for the request.

  • volume – The volume to copy.

  • image_service – The image service to use.

  • image_meta – Information about the image.


Model updates.


Creates a snapshot.


snapshot – Information for the snapshot to be created.


Create a new volume on the backend.

This method is responsible only for storage allocation on the backend. It should not export a LUN or actually make this storage available for use, this is done in a later call.

TODO(smcginnis): Add example data structure of volume object.


volume – Volume object containing specifics to create.


(Optional) dict of database updates for the new volume.


VolumeBackendAPIException – if creation failed.

create_volume_from_snapshot(volume, snapshot)

Creates a volume from a snapshot.

If volume_type extra specs includes ‘replication: <is> True’ the driver needs to create a volume replica (secondary), and setup replication between the newly created volume and the secondary volume.

An optional larger size for the new volume can be specified. Drivers should check this value and create or expand the new volume to match.

  • volume – The volume to be created.

  • snapshot – The snapshot from which to create the volume.


A dict of database updates for the new volume.


Deletes a snapshot.


snapshot – The snapshot to delete.


Delete a volume from the backend.

If the driver can talk to the backend and detects that the volume is no longer present, this call should succeed and allow Cinder to complete the process of deleting the volume.

It is imperative that this operation ensures that the data from the deleted volume cannot leak into new volumes when they are created, as new volumes are likely to belong to a different tenant/project.


volume – The volume to delete.


VolumeIsBusy – if the volume is still attached or has snapshots. VolumeBackendAPIException on error.


Any initialization the volume driver needs to do while starting.

Called once by the manager after the driver is loaded. Can be used to set up clients, check licenses, set up protocol specific helpers, etc.


context – The admin context.

extend_volume(volume, new_size)

Extend the size of a volume.

  • volume – The volume to extend.

  • new_size – The new desired size of the volume.

Note that if the volume backend doesn’t support extending an in-use volume, the driver should report online_extend_support=False.


Collects volume backend stats.

The get_volume_stats method is used by the volume manager to collect information from the driver instance related to information about the driver, available and used space, and driver/backend capabilities.

stats are stored in ‘self._stats’ field, which could be updated in ‘_update_volume_stats’ method.

It returns a dict with the following required fields:

  • volume_backend_name

    This is an identifier for the backend taken from cinder.conf. Useful when using multi-backend.

  • vendor_name

    Vendor/author of the driver who serves as the contact for the driver’s development and support.

  • driver_version

    The driver version is logged at cinder-volume startup and is useful for tying volume service logs to a specific release of the code. There are currently no rules for how or when this is updated, but it tends to follow typical major.minor.revision ideas.

  • storage_protocol

    The protocol used to connect to the storage, this should be a short string such as: “iSCSI”, “FC”, “NFS”, “ceph”, etc. Available protocols are present in cinder.common.constants and they must be used instead of string literals. Variant values only exist for older drivers that were already reporting those values. New drivers must use non variant versions. In some cases this may be the same value as the driver_volume_type returned by the initialize_connection method, but they are not the same thing, since this one is meant to be used by the scheduler, while the latter is the os-brick connector identifier used in the factory method.

  • total_capacity_gb

    The total capacity in gigabytes (GiB) of the storage backend being used to store Cinder volumes. Use keyword ‘unknown’ if the backend cannot report the value or ‘infinite’ if there is no upper limit. But, it is recommended to report real values as the Cinder scheduler assigns lowest weight to any storage backend reporting ‘unknown’ or ‘infinite’.

  • free_capacity_gb

    The free capacity in gigabytes (GiB). Use keyword ‘unknown’ if the backend cannot report the value or ‘infinite’ if there is no upper limit. But, it is recommended to report real values as the Cinder scheduler assigns lowest weight to any storage backend reporting ‘unknown’ or ‘infinite’.

And the following optional fields:

  • reserved_percentage (integer)

    Percentage of backend capacity which is not used by the scheduler.

  • location_info (string)

    Driver-specific information used by the driver and storage backend to correlate Cinder volumes and backend LUNs/files.

  • QoS_support (Boolean)

    Whether the backend supports quality of service.

  • provisioned_capacity_gb

    The total provisioned capacity on the storage backend, in gigabytes (GiB), including space consumed by any user other than Cinder itself.

  • max_over_subscription_ratio

    The maximum amount a backend can be over subscribed.

  • thin_provisioning_support (Boolean)

    Whether the backend is capable of allocating thinly provisioned volumes.

  • thick_provisioning_support (Boolean)

    Whether the backend is capable of allocating thick provisioned volumes. (Typically True.)

  • total_volumes (integer)

    Total number of volumes on the storage backend. This can be used in custom driver filter functions.

  • filter_function (string)

    A custom function used by the scheduler to determine whether a volume should be allocated to this backend or not. Example:

    capabilities.total_volumes < 10

  • goodness_function (string)

    Similar to filter_function, but used to weigh multiple volume backends. Example:

    capabilities.capacity_utilization < 0.6 ? 100 : 25

  • multiattach (Boolean)

    Whether the backend supports multiattach or not. Defaults to False.

  • sparse_copy_volume (Boolean)

    Whether copies performed by the volume manager for operations such as migration should attempt to preserve sparseness.

  • online_extend_support (Boolean)

    Whether the backend supports in-use volume extend or not. Defaults to True.

The returned dict may also contain a list, “pools”, which has a similar dict for each pool being used with the backend.


refresh – Whether to discard any cached values and force a full refresh of stats.


dict of appropriate values (see above).

initialize_connection(volume, connector, initiator_data=None)

Allow connection to connector and return connection info.

  • volume – The volume to be attached.

  • connector – Dictionary containing information about what is being connected to.

  • initiator_data – (Optional) A dictionary of driver_initiator_data objects with key-value pairs that have been saved for this initiator by a driver in previous initialize_connection calls.


A dictionary of connection information. This can optionally include a “initiator_updates” field.

The “initiator_updates” field must be a dictionary containing a “set_values” and/or “remove_values” field. The “set_values” field must be a dictionary of key-value pairs to be set/updated in the db. The “remove_values” field must be a list of keys, previously set with “set_values”, that will be deleted from the db.

May be called multiple times to get connection information after a volume has already been attached.

terminate_connection(volume, connector)

Remove access to a volume.

Note: If connector is None, then all connections to the volume should be terminated.

  • volume – The volume to remove.

  • connector – The Dictionary containing information about the connection. This is optional when doing a force-detach and can be None.