Differential Backup

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What is Differential Backup?

A differential backup contains all files that have changed since the last full backup. The advantage of a differential backup is that it shortens restore time compared to a full backup or an incremental backup. However, if you perform the differential backup too many times, the size of the differential backup might grow to be larger than the baseline full backup.

Description of the Differential Backup Type

There is a significant, but sometimes confusing, distinction between differential and incremental backup.

Incremental backup stores all the new and modified files since the last full, differential or incremental backup.

Differential backup offers a middle ground by backing up all the new and modified files since the last full backup. That is where it gets its name: it backs up everything that's different since the last full backup.

Restoring a differential backup is a faster process than restoring an incremental backup because only two backup container files are needed: the latest full backup and the latest differential backup.

Backup4all uses the information it has recorded in its catalog file (".bkc") to determine whether a file has changed since the last full backup or not.

Use differential backup if you have a reasonable amount of time to perform backups. The upside is that only two backup container files are needed to perform a complete restore. The downside is if you run multiple differential backups after your full backup, you're probably including some files in each differential backup that were already included in earlier differential backups, but haven't been recently modified.

Advantages

•	Restore is faster than restoring from incremental backup

•	Backing up is faster than a full backup

•	It uses less storage space than full backup

Disadvantages

•	Restore is slower than restoring from full backup

•	Backing up is slower than incremental backup

•	It uses more storage space than incremental backup

Differential Backup Type in Backup4all

Backup4all supports the differential backup type and offers a solution for the slow backup issue.

In time, the differential can grow to a size that is equal or larger than the full version. Therefore the following options can be used to trigger the creation of a new full backup:

•	Automatically make full backup when the differential exceeds ...% of full backup size (default is 50%)

•	Automatically make full backup when the differential exceeds ... (default is 1 Mbyte)

The system calculates the backup size for the differential backup and if the selected condition is met it performs a full backup.