When you choose to cancel an Enterprise Vault agent job, all child jobs are canceled, the selected job is canceled, and any sibling, active or queued, is also canceled. If a parent job exists, it waits for all of the children jobs and then the status of the parent becomes canceled. The status of the sibling jobs that completed before the cancel request does not change and you can use their image for a restore.
If you choose to cancel a full backup that involves an Enterprise Vault SQL database (such as a directory database), then you must make sure that you exit that backup. Then you must make sure that you take a full backup before you start the next cumulative backup.