Data Transfers · External drive and disk space
What does “Waiting for drive” mean on a transfer?
Short answer: The transfer needs your external drive, which isn't connected, so it's on hold. Plug the drive in and it starts automatically; click Check drive to re-test now, or Abandon pending to cancel all such transfers.
The transfer uses your external drive, and the drive isn't connected right now, so it's on hold rather than failing. As soon as you plug the drive back in, the transfer goes back into the queue and starts on its own. Nothing is lost while it waits.
If you've reconnected the drive and it's still waiting, select the transfer and click Check drive to re-test straight away. To give up on every transfer waiting for the drive, click Abandon pending in the toolbar.
Related: Check drive and Abandon pending · External drives