Abstract: A transactional file system performs multiple file system operations as part of a user-level transaction. An application specifies that operations should be handled as part of a transaction, and the application is given a file handle associated with the transaction context. Operations are managed consistent with transactional behavior and data isolation is provided with multiple versions of a file and by tracking copies of pages that have changed. Transactional readers do not receive changes to a file made by transactional writers, until the transactional writer commits the transaction and the reader reopens the file. Logging and recovery are also facilitated by logging page data separate from the main log, with a unique signature that enables the log to determine whether a page was fully flushed to disk prior to a system crash. Namespace isolation is also provided until a transaction commits via isolation directories.