[one-users] [OpenNebula 3.6] Problem with persistent images using FileSystem DM & qcow2 TM

[Anton Gulenko]

Dear OpenNebula community,

We are using OpenNebula 3.6 to set up a private cloud for a university
research project.
We use the FileSystem Datastore Manager and the qcow2 Transfer Manager.
For the preparation of VMs, it is important for us to use persistent images.
Using non-persistent images posed no problems at all. However,
persistent deploying a VM with a persistent image would not work.

Inspecting the scripts in the $ONE_LOCATION/var/remotes/tm/qcow2
directory, we noticed, that persistent images are handled the same way
as by the Shared Transfer Manager: by creating a filesystem-link from
the image-datastore into the System-datastore.
Is that really the intention of the ln-script in the qcow2 Transfer
Manager? We had expected a 'qemu-img create' command.
We also noticed, that the mvds-script, that is responsible for
committing the changes of the VM-disk back into the datastore, is
using the 'qemu-img convert' command.
We expected it to use the 'qemu-img commit' command, so that the
changes are pushed back into the backing image-file.

Did we misunderstand the purpose of the mentioned scripts?

By making the following changes to the scripts, we got the qcow2
Transfer Manager running just the way we expected it to:
- Delete the original ln-script and replace it with a copy of the clone-script
- Replace the 'qemu-img convert' command in the mvds-script with an
appropriate 'qemu-img commit' command

Best regards,
Anton and Frank