Comment 1 for bug 1697580

Are you waiting for each volume to show up as "in-use" before attaching another one?

Are you passing in the device_name field and expecting that to be honored when attaching the volume? Because with the libvirt driver it won't be:

https://developer.openstack.org/api-ref/compute/?expanded=attach-a-volume-to-an-instance-detail#attach-a-volume-to-an-instance

"Name of the device such as, /dev/vdb. Omit or set this parameter to null for auto-assignment, if supported. If you specify this parameter, the device must not exist in the guest operating system. Note that as of the 12.0.0 Liberty release, the Nova libvirt driver no longer honors a user-supplied device name. This is the same behavior as if the device name parameter is not supplied on the request."

Also see: https://review.openstack.org/#/c/452546/