Because the amount of time for a backup will vary each night, the number of backup media will also vary each night. Although the amount of time varies, it is still less than the times required for a differential backup during the span of a week.

When a differential backup is performed, the files that have the Archive attribute turned on are backed up, but the attribute is not turned off when the files are backed up.

With the same files and the days on which they are changed which they are changed as before, the backup schedule is performed each night starting on Sunday with a full backup, which turns the Archive attribute off on all files.

On Monday, files 2 and 5 are changed which means they will be backed up on Monday night. However, because their Archive attributes are not turned off, these files continue to be backed up every night for the rest of the week. This means that the time required to back up the files and the number of media required to write the files will increase.

On Tuesday, files 3 and 5 are modified, but because the Archive attribute on file 5 is already on, the file is again ready to be backed up. Therefore, on Tuesday night, files 2, 3, and 5 are backed up during the differential backup. For the rest of the week then, files 2, 3, and5 are backed up.

This means that each day more and more files are backed up. This requires more time to back up the files and also more backup media. By the end of the week, the backups are almost equal to the time and media required to perform a full backup.

As the week goes on, the differential backup requires more and more time and media, whereas the incremental backup uses a minimal amount of time and media, depending on the day.

Depending on your requirements for backing up your organization’s data, you should choose incremental backups if you need to take a short amount of time to perform the backups. If a full backup takes to long and the time to restore files is not an issues, the differential backups should be performed.

[tags]diana huggins,data protection,disaster planning & recovery,data loss,backup plan[/tags]