= An incremental backup method only backs up the data that has changed since the last backup, whether it was a full or an incremental backup. This method requires the least amount of time and storage space for backup, but it requires the most time to restore data for an application. To restore data from an incremental backup, the latest full backup and all the subsequent incremental backups are needed. A full backup method backs up all the data in a system or an application at a point in time. This method requires the most amount of time and storage space for backup, but it requires the least time to restore data for an application. To restore data from a full backup, only the latest full backup is needed. A differential backup method backs up the data that has changed since the last full backup. This method requires more time and storage space for backup than the incremental method, but less than the full backup method. It also requires less time to restore data for an application than the incremental method, but more than the full backup method. To restore data from a differential backup, the latest full backup and the latest differential backup are needed. A disk mirroring method creates an exact copy of a disk on another disk in real time. This method provides the highest level of availability and fault tolerance, but it also requires twice the amount of disk space. To restore data from a disk mirroring method, the mirrored disk can be used as the primary disk in case of a failure. Reference = CISM Review Manual 15th Edition, page 201-202.
The method that requires the MOST time to restore data for an application is a Full Backup. Full backups contain all the data that is required to restore an application, but the process of restoring the data is the most time-consuming as it involves copying all the data from the backup to the application. Incremental backups only backup the changes made since the last backup, differential backups only backup changes made since the last full backup, and disk mirroring provides real-time data replication, so the data is immediately available.