Description:  These systems may be considered 'inaccessible' under the new FRCP, but should be identified and addressed within the discovery process. Enterprise backup systems can be used on primary data storage systems, both Structured and Unstructured, as well as local computers on the network. They operate on either a 'snapshot' or continuous basis. Snapshots are a full or incremental image of the system while continuous backup uses transactional logs to track all changes on the system. Backup systems usually retain this information for a fixed period of time before the ESI is overwritten. The backup retention period and the relative uniqueness of the ESI on the backup media is critical to establishing metrics of discovery on these systems.