“I want to backup an SQL server, resulting in one compressed file by database.”
This is a very classical use case of evQueue. This workflow takes 4 arguments : hostname, user, password and output directory to store backups.
It is possible to run the workflow on a remote machine using the "Remote" tab in workflow launching dialog.
You can download the resulting workflow here : database_backup.xml.
It is possible to manage concurrency for each type of task (dumping or compressing) by assigning a dedicated queues to these tasks. From there you only need to adjust you newly created queues concurrency.