Driver concept

Initialize Connection

• Return remote connector if requested through volume admin metadata
  • use configured target driver
  • e.g. connecting the source of a clone target, host-assisted volume migration, backup, …
• Return local connector if connector indicates connection from same host as volume
• Transfer volume to destination and return a local connector

sequenceDiagram
  box volume host
  participant a as cinder-volume
  end
  participant db as Database
  box connector host
  participant b as cinder-volume
  end
  a->>+a: ...
driver.initialize_connection()
  opt connector host is not volume host
    a->>db: Create volume
 object for Host B
    a->>b: create_volume()
    b->>+b: ...
driver.create_volume()
    b->>b: Create lv
    b->>b: Create linear target
    b->>db: get source volume by id from admin metadata
    b->>db: update admin metadata of source volume
 to request remote connection
    b->>a: update_attachment()
Create attachment for source volume
    a->>+a: ...
driver.initialize_connection()
    a->>-a: target_driver.initialize_connection()
    a->>b: return connection_info
    b-->>a: connector.connect_volume()
    b->>b: Create metadata lv
    b->>b: load clone target
    opt this is the first attachment
      b->>-b: enable hydration
    end
    loop until volume.status == "available"
      a->>db: refresh()
    end
    a->>db: switch volume name_id,
 attributes, attachments
  end
  a->>-a: return local connector

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