You see disk usage on BOSH Director keeps growing for 7 days because BOSH Director tasks_cleanup_schedule is every 7 days at midnight, which was introduced in Operations Manager (Ops Manager) 2.10.1. The scheduled task cleans up complete BOSH tasks. For more information on this feature, refer to Ops Manager v2.10.1.
-[Fix] BOSH task cleanup occurs daily (rather than weekly). This change may alleviate issues seen in deployments where the BOSH Director runs tasks frequently (e.g. for monitoring)