What increment chains are
An increment chain is 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 31 levels of incremental backup operations.
There are two types of increment chains:
- A consecutive increment chain, which is a sequence of incremental backups that starts with level 0 and is raised by 1 at each subsequent backup.
- A nonconsecutive increment chain, where 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 are based on the most recent lower-level backup. For example, the sequence of backup levels 0, 2, 3, 1, 4 provides two increment chains: 0, 2, 3 and 0, 1, 4. The following table explains the bases of the incremental backups:
| Backup order | Increment level | Increment chain | Base | Files backed up |
|---|---|---|---|---|
| 1 | 0 | Both | Files on the storage system | All files in the backup path |
| 2 | 2 | 0, 2, 3 | Level-0 backup | Files in the backup path created since the level-0 backup |
| 3 | 3 | 0, 2, 3 | Level-2 backup | Files in the backup path created since the level-2 backup |
| 4 | 1 | 0, 1, 4 | Level-0 backup, because this 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 a lower level and is more recent than the level-0, level-2, or level-3 backups | Files created since the level-1 backup |
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