Common Log File System (CLFS)
The Common Log File System (CLFS) is a special purpose file (sub)system designed for transaction logging and/or recovery. The CLFS is not a file system in the traditional meaning of a disk file system, but more of a logical (special purpose) file system that operates in combination with a disk file system like NTFS.
The CLFS uses a base log file (.blf) and one or more container files.
In Windows Vista the CLFS is implemented as a driver named: clfs.sys. User space equivalent functionality is provided by clfsw32.dll, which communicates to the driver by DeviceIoControl calls.