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Scheduling full, incremental and differential images as part of a regular backup cycle is essential for optimizing optimising the use of available storage space, protecting your computer from sudden failure and giving you the ability to recover historical data.

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Retention and consolidation of full, differential and incremental backups combined with deletion logic maintains backup set integrity by ensuring the backup chain is never broken.

The following are examples to show how retention rules operate on your backup sets....

Full backup retention 

In Full backup retention, a specified number, or age, of full backups are retained. When full backups are purged, the entire backup set is also deleted. 

F = Full
D = Differential
I = Incremental

M T W T F   M T W T F   M T W T F   M T W T F  M T W T F  M T W 
F I I I I   D I I I I   D I I I I   D I I I I  D I I I I  F I I 

e.g, Retain 1 Full backup. 

After retention, the entire previous backup set is deleted

M T W T F   M T W T F   M T W T F   M T W T F  M T W T F  M T W 
F I I I I   D I I I I   D I I I I   D I I I I  D I I I I  F I I 

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For example, Retain 4 incremental backups.
After retention, the most recent 4 incremental backups are retained. The oldest retained incremental is not be valid on its own as it requires the previous 2 incremental backups to complete the chain. To ensure backup integrity the 2 older incremental backups are consolidated with it to create a new incremental backup.
 
M T W T F   M T W T F   M T W T F   M T W T F  M T W T F  M T W 
F I I I I   D I I I I   D I I I I   D I I I I  D I I I I  F I I 
                                                   --->I  >I I  F I I


Synthetic Full / Incrementals forever 

Incrementals forever optimizes optimises backup space and time by only ever creating a single full backup. After this, incremental backups are created forever and, once the specified number of incremental backups is reached, Macrium Reflect consolidates the incremental backup into a new 'synthetic' full backup. This is also known as a Synthetic Full backup.

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The next Monday, to retain 4 Incrementals, the Full is consolidated with the first incremental to create a new Synthetic Full.

M T W T F   M
F I I I I   I
->F I I I   I

On Tuesday the consolidation step is repeated again on the next incremental image.

M T W T F   M T
  F I I I   I I
     -->F    I I   I I

This process is repeated forever. After the first Full only Incremental backups are required.

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Differential Backup Set

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