The Mirror type synchronizes two folders. New and updated files are copied from one folder to the other folder. Files that are deleted in one folder are also deleted in the other folder.
The Copy type copies new and updated files from the left to the right folder. Files that are deleted in the left folder are also deleted in the right folder.
The Partial synchronization type copies updated files from the right to the left folder. This sync type only deals with the same files, new files or deleted files will be ignored.
The Update type has the same function as the Copy type with the exception that the Update type does not delete.
The Partial mirror type has the same function as the Mirror type with the exception that the Partial mirror type does not delete.
Note, that Nero BackItUp cannot identify changed or renamed files during the first run. The reason is that sync information is stored in a separate file and changes are compared to this information.
You can also specify how Nero BackItUp should handle a conflict. For example: you are running a sync job using the Partial synchronization type so that updated files are copied from left to right. When a file in the right folder is newer than its counterpart on the left, a conflict occurs. Depending on your choice, Nero BackItUp will keep the specified file (either the left, the right or the newest file), does not replace the file on the right, or asks you what to do.