Differential backups fall in the middle between full backups and incremental backup. A differential backup is a backup of all changes made since the last full backup. With differential backups, one full backup is done first and subsequent backup runs are the changes made since the last full backup. The result is a much faster backup then a full backup for each backup run. Storage space used is less than a full backup but more then with Incremental backups. Restores are slower than with a full backup but usually faster then with Incremental backups
Example of A Differential Backup
You setup a differential backup job or task to be done every night from Monday to Friday. Assume you perform your first backup on Monday. This first backup will be a full backup since you haven’t done any backups prior to this. On Tuesday, the differential backup will only backup the files that have changed since Monday and any new files added to the backup folders. On Wednesday, the files changed and files added since Monday’s full backup will be copied again. While Wednesday’s backup does not include the files from the first full backup, it still contains the files backed up on Tuesday.
Advantages
- Much faster backups then full backups
- More efficient use of storage space then full backups since only files changed since the last full backup will be copied on each differential backup run.
- Faster restores than incremental backups
Disadvantages
- Backups are slower then incremental backups
- Not as efficient use of storage space as compared to incremental backups. All files added or edited after the initial full backup will be duplicated again with each subsequent differential backup.
- Restores are slower than with full backups.
- Restores are a little more complicated then full backups but simpler than incremental backups. Only the full backup set and the last differential backup are needed to perform a restore.