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Reason: Macrium Reflect uses the Disk Identifier in MBR, or the Disk GUID on GPT systems, to uniquely identify the disk and verify that the backup set and backup source are of the same disk layout. These values remain stable so are a reliable identifier.

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If

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there are no matching File and Folder backup sets in the target folder

Example: Suppose you are backing up *.doc in C:\ImportantData\. with 'Strict' enabled for matching logic. You then modify the backup definition to back up *.doc;*.xls in C:\ImportantData. Reflect will then create a new full backup.

Reason: Changing the directory or filter essentially changes the source definition . In many circumstances it would not make sense to take an incremental from this source, so Reflect defaults to a new full.

File and Folder backup matching logic explained

When creating an incremental or Differential File and Folder backup the backup target folder is scanned for backup set candidates that the new Incremental or Differential backup can be appended to.  If none can be found then a new backup set is created by creating a Full backup. In v5 the matching logic checked for existing backup sets that had exactly the same root folders to backup and exactly the same selection/filter criteria. This caused a problem if a folder was added to a backup definition or if the include/exclude filters were changed. A new Full backup would always be created. In v6 there are now 3 types of matching logic that can be applied to backup definitions:

1. 1. Similar - Match on backups with at least one matching folder. Select this option to match if a backup set is found with at least one folder that is selected in the current backup. This option allows you to add and remove folders to your backup definition and still maintain a single backup set.
   2. Strict - Match on backups with the same folders and filters (As Macrium reflect v5). Select this option to match only existing backups that have exactly the same Folder and Include/Exclude Filters. This is similar to the way Macrium Reflect v5 worked.  Retention rules will only be applied to exact matched backup sets.
   3. All - Match on any backup. Select this option to match on any existing File and Folder backup set in the target folder. When selected, the most recent backup set will be appended to regardless of the folders in the set. Retention rules will be applied to all File and Folder backups.

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