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Description of Full, Incremental, and Differential Backups

Article ID: 136621 - View products that this article applies to.

This article was previously published under Q136621

SUMMARY

This article describes full, incremental, and differential backups. The Backup tool in Windows 95 supports full and incremental backups. Differential backups are not supported.

Backup uses backup file sets to help you manage backing up drives, folders, or files. Incremental and differential backups rely on an initial full backup of the drives, folders, or files in question.

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MORE INFORMATION

Many Windows 3.1-based backup programs use the archive bit to mark files that have been backed up. Backup does not use the archive bit in any way. The decision as to whether or not a file should be backed up in an incremental backup is based on the filename, its last modified date, and the date of the last incremental backup, all of which are stored in the file set.

Full Backup (or Reference Backup)

When you set the Backup Type setting to Full, all the files and folders on the drive are backed up every time you use that file set. To set the backup type, click Options on the Settings menu, and then click the Backup tab.

Example:

In Backup, click the drives, files, or folders to back up, and then click Next Step.
Click the destination (where you want the files backed up to).
On the Settings menu, click Options, click the Backup tab, click "Full: backup of all selected files," and then click OK.
On the File menu, click Save As and name your backup set. Once saved, click Start Backup.
Provide a name for the selected drive, files, or folders in the Backup Set Label dialog box, and then click OK.

Advantages:

All files from the selected drives and folders are backed up to one backup set.
In the event you need to restore files, they are easily restored from the single backup set.

Disadvantages:

A full backup is more time consuming than other backup options.
Full backups require more disk, tape, or network drive space.

Incremental Backup

An incremental backup provides a backup of files that have changed or are new since the last incremental backup. To start the process, a file set with the incremental option selected is used to perform a backup. You can select the backup type by clicking Options on the Settings menu, and then clicking the Backup tab.

For the first incremental backup, all files in the file set are backed up (just as in a full backup). If you use the same file set to perform a incremental backup later, only the files that have changed are backed up. If you use the same file set for a third backup, only the files that have changed since the second backup are backed up, and so on.

In Backup, you can select files and/or folders to be backed up. If you select a folder, all the files and folders within that folder are selected. In an incremental backup, if you select a folder, files that are added to the folder are included during the next backup. If you select specific files, files that are added to the folder are not included during the next backup.

Example:

Monday - Perform the first incremental backup of selected files and/or
         folders using a file set with the Incremental option enabled.

Tuesday - Perform another backup with the backup file set you created
          Monday. Only files that have changed since Monday's backup are
          backed up.

Wednesday - Perform another backup with the backup file set you created
            Monday. Only files that have changed since Tuesday's
            incremental backup are backed up.

To reset a file set so that the next backup backs up all files, and not just files that are new or have changed, follow these steps:

On the File menu, click Open File Set. Click the file set you want to use, and then click Open. Click Next Step.
Click the destination (where you want the files backed up to).
On the Settings menu, click Options, click the Backup tab, click "Full: backup of all selected files," and then click OK.
On the File menu, click Save to save your backup set.
Repeat steps 1 and 2.
On the Settings menu, click Options, click the Backup tab, click "Incremental: backup of selected files that have changed since the last full backup," and then click OK.

Advantages:

Backup time is faster than full backups.
Incremental backups require less disk, tape, or network drive space.
You can keep several versions of the same files on different backup sets.

Disadvantages:

In order to restore all the files, you must have all of the incremental backups available.
It may take longer to restore a specific file since you must search more than one backup set to find the latest version of a file.

Differential Backup (Not Supported in Backup)

A differential backup provides a backup of files that have changed since a full backup was performed. A differential backup typically saves only the files that are different or new since the last full backup, but this can vary in different backup programs. Together, a full backup and a differential backup include all the files on your computer, changed and unchanged.

Example:

Monday - Perform a full backup and save the file set.

Tuesday - Perform a differential backup using the same file set. All files
          that have changed since the full backup are backed up in the
          differential backup.

Wednesday - Perform a differential backup using the same file set. All the
            files that have changed since Monday's full backup are backed
            up.

Advantages:

Differential backups require even less disk, tape, or network drive space than incremental backups.
Backup time is faster than full or incremental backups.

Disadvantages:

Restoring all your files may take considerably longer since you may have to restore both the last differential and full backup.
Restoring an individual file may take longer since you have to locate the file on either the differential or full backup.

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