Which type of backup saves only the files that have changed since the last full backup?

The correct answer identifies the concept of a differential backup. This type of backup is designed to save only the files that have changed since the last full backup. When a differential backup is performed, it captures all changes made after the last full backup, regardless of any intermediate backups that may have taken place. This approach allows for a more efficient backup process compared to a full backup, as it reduces the amount of data that needs to be stored and transferred upon each backup run.

In a typical backup strategy, the differentiation between backup types is key. For instance, a full backup captures everything each time it is done, which means it can take longer and consume more storage space. Incremental backups, on the other hand, save only the data that has changed since the last backup of any type, whether that be a full or an incremental backup. This means incremental backups can become complex, as restoring requires the last full backup and all subsequent incremental backups. Snapshot backups capture the state of the system at a particular point in time but do not fit the definition of a backup that targets changed files relative to a prior full backup.

Understanding how differential backups function is crucial for effective data management and recovery strategies, as they balance efficiency with restoration speed and complexity.