Allow an attached volume to be extended

https://blueprints.launchpad.net/nova/+spec/nova-support-attached-volume-extend

Problem description

Currently a volume size extension requires that a volume be in the available state. This requires an attached volume to be detached from a server before the volume can be extended in size. This requires that a volume be brought offline from the standpoint of the application using the volume.

Use Cases

A end user wants to increase the size of a volume that is currently attached to a server.

Proposed change

Nova will be listening for attached volume extend notification from Cinder using the existing external-events API endpoint.

When the notification is received, Nova will trigger a rescanning of device on the host using os-brick to discover the change in volume size. The os-brick library already supports volume size extension through the Connector API method called “extend_volume” since 0.8.0.

The initial implementation aims to support virt drivers using os-brick such as libvirt and hyper-v.

The end user will have to perform a partition and/or filesystem resize in the guest to fully benefit from the new volume size.

Capabilities discovery and error handling if the compute host does not support the extend volume operation are being discussed on the openstack-dev mailinglist. [1]

Alternatives

None

Data model impact

None

REST API impact

A new microversion is required because a new external-event type will be added: volume-extended.

Proposed JSON request body for the new “volume-extended” event:

{
    "events": [
        {
            "name": "volume-extended",
            "server_uuid": "3df201cf-2451-44f2-8d25-a4ca826fc1f3",
            "tag": "0e63d806-6fe4-4ffc-99bf-f3dd056574c0"
        }
    ]
}

Definition of fields:

name

Name of the event. (“volume-extended” for this feature).

tag

Volume UUID being extended.

server_uuid

Server UUID to which the extended volume is attached.

Proposed JSON response body for the new “volume-extended” event:

{
    "events": [
        {
            "name": "volume-extended",
            "status": "completed",
            "code": 200,
            "server_uuid": "3df201cf-2451-44f2-8d25-a4ca826fc1f3",
            "tag": "0e63d806-6fe4-4ffc-99bf-f3dd056574c0"
        }
    ]
}

Definition of fields:

name

Name of the event. (“volume-extended” for this feature).

status
Event status. Possible values:

  • “completed” if accepted by Nova

  • “failed” if a failure is encountered

code
Event result code. Possible values:

  • 200 means accepted

  • 404 means the server could not be found

  • 422 means the event cannot be processed because the instance was found to not be associated to a host.

server_uuid

Same value as provided in original request.

tag

Same value as provided in original request.

Possible HTTP response codes:

  • The HTTP response code 200 is returned on success.

  • The HTTP response code 207 is returned if any event fails with 422 code.

  • The HTTP response code 400 is returned on a bad request.

  • The HTTP response code 401 is returned if request is unauthorized. (keystone)

  • The HTTP response code 403 is returned if request is forbidden. (policy)

  • The HTTP response code 404 is returned if no server could be found.

Security impact

None

Notifications impact

None

Other end user impact

The end user will be able to extend their volumes without having to detach them.

The end user will have to perform a partition and/or filesystem resize to fully benefit from the new volume size.

Performance Impact

None

Other deployer impact

None

Developer impact

Driver owners may want to enable this feature in their driver.

Implementation

Assignee(s)

Primary assignee:

mgagne

Other contributors:

manas-mandlekar shyvenug@in.ibm.com

Work Items

  • Add new external-event type and new microversion

  • Call virt driver so guest detects the new volume size

  • Call the os-brick extend_volume API to trigger the host kernel size information to be updated on the attached host

Dependencies

  • The Cinder API changes to allow extend of an attached volume

Testing

Add Tempest test where the size of a volume attached to a server is extended and the new size can be discovered on the host.

Documentation Impact

Update the compute API reference documentation with new volume-extended event.

References

This blueprint is in conjunction with the work being done on the Cinder extend attached volume. [2]

History

Revisions

Release Name

Description

Pike

Introduced