HP UX Common Internet File System (CIFS) Client/Server Software manual

Chapter 9 CIFS/9000 File Locking Interoperability Summary

A CIFS/9000 server can provide file storage (and printing) for Windows clients, UNIX clients, NFS and PC-NFS clients, and the CIFS/9000 client. Understanding how the various client platforms invoke file locking for homogenous and heterogeneous (mixed) client access is critical when designing and implementing a NAS or technical server configuration.

It is absolutely essential that HP sales force personnel understand the customer environment to determine if cross-platform file locking is a necessity. It is also essential that the customer understand that competitor’s claims of protection from non-locking NFS clients does not provide comprehensive data integrity, because if one non -locking NFS client can access a file, then two non-locking NFS clients can access a file, and no vendor can claim data integrity protection for two non -locking clients.

CIFS/9000 provides secure, comprehensive file locking for homogenous Windows client access

–either locally or over an NFS mount. Mixed client access requires knowledge of how the various client platform applications and file systems lock files to fully understand how they will interoperate. Based upon that knowledge, informed decisions can be made about how to configure the CIFS/9000 for mixed client access, or whether to allow mixed client access, or whether CIFS/9000 is the correct server platform to implement.

Windows utilizes 3 different file locking mechanisms:

Mandatory Share Mode (Open Mode) Locking

Byte Range Locking

Opportunistic Locking (Oplocks)

Windows clients unilaterally honor mandatory share mode (open mode) and byte range locking. Opportunistic locking allows Windows clients to cache files locally, thus enjoying a significant performance boost due to decreased network latency. Oplocks rely on the ability of an oplock break to notify the caching client that concurrent access has been requested from another client, therefore causing the original client to flush all cached data to the file server.

UNIX/NFS uses Byte Range locking to implement the advisory locking protocol. UNIX/NFS locking is not mandatory in most cases, and requires that other processes correctly implement the advisory locking protocol. Byte range locking in this case does not protect a file from non-locking UNIX/NFS processes.

PC-NFS (as tested with WRQ) utilizes the Network Lock Manager to implement byte range locking. Thus, PC-NFS also is dependant upon the advisory locking protocol for concurrent file access, and cannot protect a locked file from access by a non-locking process.

CIFS/9000 implements all aspects of Windows file locking when file access is homogeneous, Windows-only access.

CIFS/9000 at first release provides interoperability between Windows, UNIX/NFS, and PC- NFS clients by implementing the byte range advisory locking protocol. CIFS/9000 will

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