We have a DD670 with a ES30 added on.  It shows 18.39 TB available /data:post-comp.

Active Tier shows 10.9TB.

We plan to use it as a media device for Commvault to store backups on.

What does this Tier stuff mean?  What happens when we exceed 10.9TB?  Does it get moved?  Do I need another license to use the rest of the space?