The update log area stores a history of file system structure changes for high-speed file system recovery. This area is maintained as a cyclic log.
The update log area contains data about the following processes:
Acquiring or releasing an i-node
Updating i-node data
Allocating or releasing an extent, which is a group of contiguous file system data blocks handled as a single unit
Acquiring or releasing V-data
Updating V-data
The GFS Shared File System assures that data is written in the V-data area before the file system structure is updated. If a system failure occurs, file system consistency is restored by using sfcfsck(8) to either invalidate or re-execute unprocessed changes on the file system. Also, system failure recovery processing is conducted. Only changes to the file system structure are recorded in the update logs; file-data is not recorded.
