Drew Thorstensen f7de66aac0 Dev-ref update

This change set provides a significant update to the nova-powervm
drivers dev-ref.

Rebases the documentation to reflect the development that has been done
over the last several months.  Updates the readme to reflect the
execution that has completed.

Removes the fake_driver that is not useful.

Change-Id: I1910db886df89f884f3c399d6aab1eebdf10b5e0

2015-10-08 15:09:42 -04:00

3.8 KiB

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Source Code Structure

Since nova-powervm strives to be integrated into the upstream Nova project, the source code structure matches a standard driver.

nova_powervm/
  virt/
    powervm/
      disk/
      tasks/
      volume/
      ...
  tests/
    virt/
      powervm/
        disk/
        tasks/
        volume/
        ...

nova_powervm/virt/powervm

The main directory for the overall driver. Provides the driver implementation, image support, and some high level classes to interact with the PowerVM system (ex. host, vios, vm, etc...)

The driver attempts to utilize TaskFlow for major actions such as spawn. This allows the driver to create atomic elements (within the tasks) to drive operations against the system (with revert capabilities).

nova_powervm/virt/powervm/disk

The disk folder contains the various 'nova ephemeral' disk implementations. These are basic images that do not involve Cinder.

Two disk implementations exist currently.

localdisk - supports Virtual I/O Server Volume Groups. This configuration uses any Volume Group on the system, allowing operators to make use of the physical disks local to their system.
Shared Storage Pool - utilizes PowerVM's distributed storage. As such this implementation allows operators to make use of live migration capabilities.

The standard interface between these two implementations is defined in the driver.py. This ensures that the nova-powervm compute driver does not need to know the specifics about which disk implementation it is using.

nova_powervm/virt/powervm/tasks

The task folder contains TaskFlow classes. These implementations simply wrap around other methods, providing logical units that the compute driver can use when building a string of actions.

For instance, spawning an instance may require several atomic tasks:

Create VM
Plug Networking
Create Disk from Glance
Attach Disk to VM
Power On

The tasks in this directory encapsulate this. If anything fails, they have corresponding reverts. The logic to perform these operations is contained elsewhere; these are simple wrappers that enable embedding into Taskflow.

nova_powervm/virt/powervm/volume

The volume folder contains the Cinder volume connectors. A volume connector is the code that connects a Cinder volume (which is visible to the host) to the Virtual Machine.

The PowerVM Compute Driver has an interface for the volume connectors defined in this folder's driver.py.

The PowerVM Compute Driver provides two implementations for Fibre Channel attached disks.

Virtual SCSI (vSCSI): The disk is presented to a Virtual I/O Server and the data is passed through to the VM through a virtualized SCSI connection.

N-Port ID Virtualization (NPIV): The disk is presented directly to the VM. The VM will have virtual Fibre Channel connections to the disk, and the Virtual I/O Server will not have the disk visible to it.

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