Incremental backup

Incremental backup provides a faster method of backing up data than repeatedly running full backups. During an incremental backup, only files changed since the most recent backup are included. That is where it gets its name: each backup is an increment for a previous backup.

The representation below shows how a backup job running four times would look like when using incremental:

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The time it takes to execute the backup may be a fraction of the time it takes to perform a full backup. Backup4all is a backup program that supports incremental backup, and it uses the information recorded in its catalog file (.bkc) to determine whether each file has changed since the most recent backup.

The advantage of lower backup times comes with a price: increased restore time. When restoring from incremental backup, you need the most recent full backup as well as EVERY incremental backup you've made since the last full backup.

For example, let's assume you did a full backup on Friday and incremental backups on Monday, Tuesday and Wednesday. If you need to restore your backup on Thursday morning, you would need all four backup container files: Friday's full backup plus the incremental backup for Monday, Tuesday and Wednesday. By comparison, if you had run differential backup on Monday, Tuesday and Wednesday, then to restore on Thursday morning you would have needed only Friday's full backup plus Wednesday's differential.

Advantages of incremental backups:

1. It is the fastest backup type since it only backs-up increments
2. Saves storage space compared to other types
3. Each backup increment can store a different version for a file/folder

Disadvantages for this backup type:

1. Full restore is slow compared to other backup types (you need the first full backup and all increments since then)
2. To restore the latest version of an individual file the increment that contains it must be found first

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Backup4all supports incremental backups and offers a solution for the slow restore disadvantage.
To keep the number of stored increments to a reasonable value and reduce the size of the backups, Backup4all provides two options: "Limit the number of stored backups" and "Merge stored backup to maintain the maximum limit" that can limit the number of stored backups. These two options will perform an internal merge to keep the number of stored incremental backups under the selected limit.