Hi I have a question regarding when steps are able to run in parallel. We noticed that sometimes all of the jobs from a scatter must complete before moving to the next 

I was wondering whether a scattered subworkflow can start before all the inputs to that step are available, or does a subworkflow have to wait for all of the previous inputs to be available regardless of whether they are available for **just the first set** of scattered inputs?
All inputs for the step have to be available. See [this][1], look for bullet point "Instead of scattering separate steps, prefer to scatter over a subworkflow."


  [1]: https://doc.arvados.org/user/cwl/cwl-style.html