Backup Terms and Definitions

Are you confused about the terminology used by the storage industry concerning backup systems? Research conducted by Teradactyl indicates you are not alone. Many of the storage vendors and trade publications are using the following terms in different and often conflicting ways. One of the most obvious errors is the common misuse of Incremental and Differential terms. We went to the National Institute of Standards and Technology (NIST) and other reputable sources to confirm the accuracy in our use of the terminology. Teradactyl has compiled a list of backup definitions for reference by anyone interested or involved in the backup storage market. The references contained herein are going to be enhanced to include additional approaches to backup that augment methods of data collection but do not mitigate these definitions. Please return to these resources for more information!

Primary Storage

This is data that is being protected. The data backed up is not just file data, it also includes meta data such as directories, folders, filenames, file attributes, access control lists and other security information. Primary storage typically includes entire data partitions, but may also include specific sub-directories or individual files.

Backup Volume

Data that is replicated from Primary Storage to an alternate location.

Secondary Storage

Typically media devices such as disk and tape which are responsible for the storage of Backup Volumes. Secondary Storage may be directly attached to systems with Primary Storage, network attached, or locally attached to a Backup System.

Backup System

A system that is responsible for coordinating the backup and restore processing and providing Secondary Storage for data.


Three Ways Backups Can Occur

Direct Backups

Primary Storage is copied to Secondary Storage which is directly attached to the Primary Storage system.

Network Backups

Primary Storage is copied to a remote storage system via a network connection. Remote storage systems may be attached to the network or directly attached to the Backup System.

Synthetic Backups

Uses existing Backup Volumes within the Backup System to generate new Backup Volumes without the need to access Primary Storage. Synthetic Backups minimize the impact of the backup function on Primary Storage by eliminating the need to recopy data that has already been backed up. This savings extends to network resources when backups from Primary Storage occur over a network.


Full Backups

Full Backups

Level 0: In a full or epoch backup, all of the Primary Storage on a target system is backed up. The data backed up in a Full Backup includes file data and meta data such as directories, folders, filenames, file attributes, access control lists and other security information.

Direct Attached Full

A type of Full Backup that copies Primary Storage on a target system to directly attached Secondary Storage on the target system.

Network Full

A type of Full Backup that copies Primary Storage on a target system over a network to Secondary Storage.

Synthetic Full

A type of Full Backup that consolidates Incremental Backups (see below) with a previous Full Backup to produce a current Full Backup. This process is performed by a backup system with no interaction with the target system. The resulting backup volume contains the same data as one that would have been taken from the target system at that point in time.


Incremental Backups

Incremental Backups

Level 1 through 9:
An Incremental Backup will only backup the files that have been modified or created since any previous backup. Incremental Backups represent data changes between two points in time.

Four Categories of Incremental Backups:

Cumulative Incremental

Level n: A Cumulative Incremental Backup will backup the files that have been modified or created since the most recent lower level backup (level n-1 or lower).

  • Direct Cumulative Incremental: A Cumulative Incremental backup that copies Primary Storage on a target system to directly attached Secondary Storage on the target system.
  • Network Cumulative Incremental: A Cumulative Incremental backup that copies Primary Storage on a target system over a network to Secondary Storage.
  • Synthetic Cumulative Incremental: A special type of Cumulative Incremental that will consolidate some or all of the Backup Volumes that have been created since the most recent backup at level n-1 or lower on the Backup System. This process is performed by a Backup System with no interaction with the Primary Storage on the target system. The resulting backup volume contains the same data as one that would have been taken from the target system for that period of time.

More information on Cumulative Incremental Backups...

Differential Backup

Level 1: A special type of Cumulative Incremental Backup that copies the files that have been modified or created since a previous Full Backup.

  • Direct Differential: A Differential Backup that copies Primary Storage on a target system to directly attached Secondary Storage on the target system.
  • Network Differential: A Differential Backup that copies Primary Storage on a target system over a network to Secondary Storage.
  • Synthetic Differential: A special type of Differential that will consolidate some or all of the Backup Volumes that have been created since the most recent full backup on the Backup System. This process is performed by a Backup System with no interaction with the Primary Storage on the target system. The resulting backup volume contains the same data as one that would have been taken from the target system for that period of time.

More information on Differential Backups...

Partial-Cumulative Incremental Backup

Level n: A specialized form of Incremental Backup which backs up the files that have been modified or created since the most recent backup at the same level or lower (level n or lower).

  • Direct Partial-Cumulative Incremental: A type of Partial Cumulative Incremental Backup that backs up Primary Storage on a target system to directly attached Secondary Storage on the target system.
  • Network Partial-Cumulative Incremental: A type of Partial Cumulative Incremental Backup that backs up Primary Storage on a target system over a network to a Secondary Storage.
  • Synthetic Partial-Cumulative Incremental: A special type of Partial Cumulative Incremental that will consolidate some or all of the Backup Volumes that have been created since the most recent backup at level n or lower on the Backup System. This process is performed by a Backup System with no interaction with the Primary Storage on the target system. The resulting backup volume contains the same data as one that would have been taken from the target system for that period of time.

More information on Partial-Cumulative Incremental Backups...

True incremental Backup

A special type of Direct or Network Partial Cumulative Incremental Backup. A True incremental backup will only backup the files that have been modified or created since the most recent backup from the client. Note: The last client backup could be at any level.

More information on True incremental Backups...