How to Restore a Differential Backup
The differential backup method is a good “interim” method to use between full backups, because it only backs up new or changed data since the last full or incremental backup. This is an efficient use of time and space, and is effective for saving any new or modified files until the next full backup. The disadvantage of this method is that the restore time could be longer and more complicated, since at least two sets of data (the full backup set and the differential set, and any incremental sets in between) are involved.
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Things You'll Need
- Last full backup data set
- Any incremental data sets created between the last full backup and the target differential backup
- Target differential backup data set
Instructions
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Restore the last full backup data set. This is the “base” data set, as it includes all files (that is, all files that existed at the time of the full backup).
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Restore any incremental data sets that were created between the last full backup and the target differential backup, if applicable. Like the differential backup, an incremental backup also backs up any new or changed data since the last full backup. In contrast to the differential backup, the incremental backup clears the archive attribute, meaning that it marks the files as having been archived. The significance of this is that any future incremental or differential backups will not archive these files again, unless a change is made to the file (in which case the archive attribute will be set again). For this reason, any incremental data sets that were created after the last full backup, but before the target differential backup, will need to be restored at this point.
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Restore the differential backup set. This will update the backup data with any files that have been changed or added since the last full or incremental backup set.
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Tips & Warnings
Most backup software packages offer a variety of backup methods. These usually include the full backup method (all files), the incremental method (new or changed files since the last full or incremental backup; marks files as archived), and the differential method (new or changed files since the last full or incremental backup; does not mark files as archived). When combined appropriately, these methods can provide an effective backup strategy.
While a full backup is ideal for keeping a single, comprehensive data set, it’s not practical to rely solely on this method for large amounts of data, because a full backup carries a high cost in terms of storage space and time. A better strategy is to use a combination of the full backup and either the incremental or differential method.
If you want to restore a single file and you know the date the file was created or last modified, you may be able to restore it directly from the backup set closest to that date. Consult your backup software documentation for details.
