Comment 3 for bug 1779654

Furthermore, nova boot command which was executed in your case, basically creates a bootable volume and spawns a new nova instance from it. And that volume is attached & thus its status should be “in-use”.
In the above case, only two driver api's are invoked viz. create_volume() & initialize_connection().

There are couple of error messages seen in provided log file “cinder-volume.log.2”:
1) “Delete snapshot failed, due to snapshot busy.”
2) “2018-06-07 08:03:48.693 17974 ERROR cinder.volume.manager ImageCopyFailure: Failed to copy image to volume: Bad or unexpected response from the storage volume backend API: Unable to fetch connection information from backend: Error (HTTP 500) OPERATION_FAILED - The operation failed: The volume list 'helion-cp1-c1-m1-mgmtVolumeList1528358624' cannot be created because a volume list with the same name already exists. Enter a different name for the new volume list.”

3) 2018-06-07 08:45:57.441 30555 ERROR cinder.volume.driver [req-9bb0e9b4-33dc-4956-9a8b-baf8add719d5 45336d44e7174de5b7d0430639437ccf 7ce30e9231de44009f10b555896105d4 - default default] Unable to fetch connection information from backend: Error (HTTP 500) SERVER_ALREADY_EXISTS - The server with the name "$1" already exists. Use a unique name and try again.

>> wsapi gives the error message "SERVER_ALREADY_EXISTS" when it tries to create a SERVER which is already present in case of attachment.
but drivers handles this scenario, by first checking the SERVER existence source code link & if it’s not found then only it tries to create the new SERVER. I tried to reproduce with only python-lefthandclient & not with cinder.