differential v. incremental backup
Friday, July 30, 2010 Backing up all of the files on a computer’s hard drive requires a considerable amount of time and disk space, but most of the data stored on the drive changes slowly or not at all. Therefore, after a full backup has been made, more efficient methods can be used to backup only the files that have changed.
A differential backup backs up the files that have changed since the last full backup. For example, one might schedule a weekly full backup on Sunday, and subsequent daily differential backups. Monday’s backup would include everything that had changed since Sunday. Tuesday’s differential would also include all files that had changed since Sunday, and so on. As time elapses, and changes accumulate, differential backups get successively larger. Monday’s backup could be quite small, but Saturday’s backup could be substantially bigger. To restore data, only the last full backup and the last differential backup are required.
An incremental backup backs up the files that have changed since the last backup of any kind, whether it was full or incremental. Using a schedule like the one above, Monday’s incremental backup would cover changes since Sunday, Tuesday’s would only cover changes since Monday, and so on. To reconstitute data, the last full backup and every incremental backup since then are required.
Compared to incremental backups, differential backups are slower to backup, faster to restore, and create larger backups. Incremental backups are faster to backup, slower to restore, and create smaller backups.