# Constraints and Limitations

Note the following constraints and limitations about CSBS:

- An ECS can be associated with only one backup policy.
- Shared EVS disks in ECSs can be backed up.
- CSBS supports crash-consistent backup of EVS disks on an ECS but not application-consistent backup of them.
- CSBS does not support consistent backup of multiple ECSs.
- CSBS supports backup and restoration of all EVS disks as a whole instead of part of the EVS disks on an ECS. In addition, CSBS does not support file- or directory-level restoration.
- You are not advised to back up an ECS whose capacity exceeds 4 TB.
- Servers or disks at the disaster recovery (DR) site can be restored only when DR protection is disabled for servers deployed with Storage Disaster Recovery Service.

Parent topic: Accessing and Using CSBS