One of the significant advanced backup options is the backup type. In fact, there are a few wizards that will ask you about what type of backup to create, so it helps to know the significance of the available selections. To understand the differences between backup types, it's crucial to understand the significance of the archive bit. The archive bit is simply a marker designating whether a file has changed since the last time it was backed up. In other words, when a file changes, the archive bit is added. Then, when certain backup types back up the file, the archive bit is removed. If the file changes again, the archive bit is added once more. Clearance of the archive bit is an indicator that the file has been backed up.
There are five different backup types available with XP's Backup Utility:
Backs up all selected files and marks each file as having been backed up; that is, it clears the archive bit. This type of backup is often used as a baseline that other backup types use to determine what needs backing up. Because it backs up everything you select, the normal backup also takes the longest. But it's the easiest to restore. Many companies that shut down operation for the night perform a full nightly backup because time is not a concern.
Backs up all selected files and does not mark them as being backed up. A copy is useful as a quick way to archive a subset of working data without impacting your overall backup strategy.
Backs up only the selected files that have changed since the last normal or incremental backup and does not clear the archive bit. In other words, a differential backup does not mark files as having been backed up. These backups take longer but are quicker to restore.
Example: If you were using a differential backup strategy, you could restore after a crash by applying the last normal backup plus the most recent differential backup.
Backs up selected files that have not been marked as archived and marks the files as having been backed up. These backup types are normally much quicker than differential backups because less data is being archived. However, they take longer to restore because more differential backups must be applied to the last normal backup.
Example: If using a differential backup strategy, you could restore after a crash by using the last normal backup and then applying all incremental backups made since the normal backup.
Backs up only the selected files that have changed on the current day and does not clear the archive bit. Each daily backup and the last normal backup are required for a successful restore. The daily backup is often included in the overall backup strategy at many companies, with normal backups performed on the weekend, and daily backups each night.
Even if you're not using one of the wizards, you can still configure the backup type by choosing Options from the Tools backup menu. Click the Backup Type tab, as shown in Figure 13-5, and select the backup type in the drop-down dialog box.
Figure 13-5. Select the backup type.
You will see these backup choices crop up throughout the chapter.
So which backup type is best? Whichever one backs up your data and lets you easily restore. The best backup type depends on how much data you're backing up, how often you'll perform a backup, how quickly you want the backup to be performed, and how many backups you are willing to apply in the event of a restore.