With Data Protection for Microsoft Exchange software you can manage and configure storage management policy for backups.
Although Tivoli® Storage Manager policy determines how Data Protection for Microsoft Exchange backups are managed on Tivoli Storage Manager storage, backup retention on local shadow volumes is determined by version and time-based policies. Ensure that sufficient local storage space is available on local shadow volumes for a VSS backup. In addition, verify that there is enough available storage space assigned to the volumes to accommodate your backup operations. The shadow copy volume that is the storage destination of a snapshot must have sufficient space for the snapshot.
Environment and storage resources also affect how many backup versions are maintained on local shadow volumes. The amount of space that is required is dependent on the VSS provider that you use.