Comment 3 for bug 1497484

The reported error appears to originate from glance. Without logs it's hard to be 100% certain, but my supposition is that it's raised when nova tries to push the created snapshot to glance, and glance rejects it because it's qcow2.

The question then becomes: why is nova creating a qcow2 snapshot image? The reasons would be appear to be either that the existing disk is qcow2 (or was mis-detected as such, see bug 1524274), or that the config variable snapshot_image_format is set to qcow2. Or alternatively some other tortured reason in this organic heap of code.

This does suggest a solution, though. If you set 'snapshot_image_format' to 'raw' in nova.conf, it should always convert to raw before uploading to glance. If my original supposition is correct, this should fix your problem without any code changes.