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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.


A CLFS log consists of a base log file (.blf) and one or more container files.

There are two types of logs:

  • dedicated logs; contains a single stream of log records.
  • multiplexed (or common) logs; contains several streams of log records.


According to Wikipedia CLFS was introduced in Windows server 2003 R2.

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.

Also see

Windows Internals 5 by Mark E. Russinovich and David A. Solomon