The immutability of backups lies in their absolute inability to be modified, neither by a human nor by a program. The purpose of an immutable backup is thus to be unalterable, and therefore it cannot be encrypted, modified, or deleted.

There are several technological solutions to ensure the immutability of backups: tapes, cartridges, WORM disks, and certain types of object storage.

There are constraints and risks associated with immutability; for example, the immutability of storage inevitably leads to the retention of every new version of the object for the duration of the object’s retention period.

This data retention method will thus increase an organization’s storage costs due to additional data storage, and the organization cannot delete previous versions.