For passive routing, there is no limit to how long a system can be out of service. For managed routing sessions, the amount of time a Teradata system can be out of service for a planned outage is limited by the volume of data and SQL requests executed in managed sessions on the other active Teradata systems. The data is stored in the data file system on the Unity servers. Each Unity server has 10-15 TB of storage space available. Adding Unity servers as expansion servers can increase this space.