Real-time mirroring is implemented in a file system filter driver that performs RAID-1 type of mirroring in software on per file basis. Like a software-only RAID-1 system, it duplicates individual file I/O requests in memory and sent them to both source and mirror devices. That means same data are written to both source and mirror files at the same time whenever there is any change in the source file. Other file operations like move, rename, delete, attribute change, etc., are also performed in the mirror folder simultaneously with the source folder. So, at any point of time the content of the source and mirror folders remains identical.
For example, if you have a large database file in your source folder and modify only one record in that file using the application interface of that database, the driver included with MirrorFolder will modify only that same record in the mirror database file simultaneously, and will NOT copy the entire source database file to its mirror.