What increment chains are

An increment chain consists of a series of incremental backups of the same path. Because you can specify any level of backup at any time, you must understand increment chains to be able to perform backups and restores effectively. You can perform nine levels of incremental backup operations.

There are two types of increment chains:

A consecutive increment chain is a sequence of incremental backups that starts with level 0 and is raised by 1 at each subsequent backup.
A nonconsecutive increment chain is one in which incremental backups skip levels or have levels that are out of sequence, such as 0, 2, 3, 1, 4, or more commonly, 0, 1, 1, 1 or 0, 1, 2, 1, 2.

Incremental backups base themselves on the most recent lower-level backup. For example, the sequence of backup levels 0, 2, 3, 1, 4 gives two increment chains: 0, 2, 3 and 0, 1, 4. The following table explains the bases of the incremental backups:

Back-up order	Increment level	Increment chain	Base	Files backed up
1	0	Both	Files on the storage system	All files in the back up path
2	2	0, 2, 3	The level-0 backup	Files in the backup path created since the level-0 backup
3	3	0, 2, 3	The level-2 backup	Files in the backup path created since the level-2 backup
4	1	0, 1, 4	The level-0 backup, because that is the most recent level that is lower than the level-1 backup	Files in the backup path created since the level-0 backup, including files that are in the level-2 and level-3 backups
5	4	0, 1, 4	The level-1 backup, because it is both of a lower level and more recent than the level-0, level-2, or level-3 backups	Files created since the level-1 backup