Which feature does the NFS 4.1 client offer over NFS 3?

The NFS 4.1 client provides significant improvements over its predecessor, NFS 3, particularly in the area of file locking and access control enhancements. One of the core advancements in NFS 4.1 is the integration of mandatory file locking, which allows for better coordination when multiple clients access shared files. This feature helps prevent data corruption that can arise from concurrent access.

Moreover, NFS 4.1 introduces more robust access control mechanisms. It employs the use of the Network File System version 4 Access Control Lists (ACLs) which allow more granular permissions to be set on files and directories compared to the simpler UNIX-style permissions used in NFS 3. This helps ensure that only authorized users and applications can interact with specific files, bolstering security and data integrity.

The other options relate to features that are either enhancements not present in NFS 4.1 or aspects that do not specifically highlight the advancements made with regard to file management and security in this version. Thus, the support for enhanced file locking and access control represents a crucial and distinctive improvement of the NFS 4.1 client over NFS 3.