Abstract: Various methods and systems for implementing a file change log in a distributed file system are disclosed. In one embodiment, a method involves operating a distributed file system that presents a namespace and maintaining a file change log for the namespace. Operating the distributed file system involves executing an instance of a file system on each of several nodes. Maintaining the file change log can involve maintaining a single file change log for the namespace. Updates to the single file change log can be handled by a primary node or controlled using a locking mechanism. Alternatively, several private file change logs (e.g., one per node) can be maintained, and these private file change logs can be merged into a single file change log (e.g., by a primary node).

Abstract: A lock is acquired on a data structure. Content in the data structure is read and verified while the lock is held. The lock is then released, and then the file system components that are referred to by the data structure are verified. In essence, a file system consistency check of the file system components is performed offline in the background while the data structure remains accessible.

Abstract: A list of data structures (e.g., inodes) can be accessed, and the data structures in the list can be examined. If a data structure is examined, a counter value associated with the data structure is changed to a generation number that is associated with the examination. Subsequently, the counter values can be used to identify unreferenced data structures. More specifically, the counter value for an unreferenced data structure will be different from the generation number for the most recently performed examination.

Abstract: A lock is acquired on a data structure. Content in the data structure is read and verified while the lock is held. The lock is then released, and then the file system components that are referred to by the data structure are verified. In essence, a file system consistency check of the file system components is performed offline in the background while the data structure remains accessible.

Abstract: A list of data structures (e.g., inodes) can be accessed, and the data structures in the list can be examined. If a data structure is examined, a counter value associated with the data structure is changed to a generation number that is associated with the examination. Subsequently, the counter values can be used to identify unreferenced data structures. More specifically, the counter value for an unreferenced data structure will be different from the generation number for the most recently performed examination.