All about Backup

Differential Backup Method

There is a significant, but sometimes confusing, distinction between differential backup and incremental backup. Whereas incremental backs up all the files modified since the last full backup or incremental backup, differential backup offers a middle ground by backing up all the files that have changed (file is changed if content, attribute or access permition rights are changed) 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 all you need is the last full and last differential backup.

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.
Differential backup is gaining in popularity because it traps files at points in time, for example, prior to virus corruption.

Advantages: restore is faster than restoring from incremental backup, backing up is faster than a full backup, the storage space requirements are lower than for full backup.
Disadvantages: restore is slower than restoring from full backup, backing up is slower than incremental backup, the storage space requirements are higher than for incremental backup.

See also: Mirror Backup Method