HP CIFS File Locking Interoperation

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Chapter 3 File Locking Overview
File locking is typically initiated by the file system – either by configuration parameters or
API and function calls – to prevent data corruption by more than one process accessing a file
while it is open in write mode (either dual writes occurring, or reading a file that has since
been changed due to a write – “stale data”). There are two important factors to consider
when enabling file locking: first – when to use file locking; second – how to lock the file.
File locking provides a security and/or integrity benefit, but the benefit is not free. Locking
uses system resources, therefore it can affect performance. In addition, some kinds of locking
can actually enhance performance, but expose data to corruption under certain types of
access. Also, using file-system -provided file locking can be redundant if data is already
locked or managed at the application level, thus using system resources affecting
performance for no benefit. Finally, how data is used should partially dictate how files are
locked: if a file is to be opened read-only, then locking the file may not make much sense.
HP Sales Force personnel often encounter RFPs that include CIFS/NFS cross-platform file
locking as a requirement. It is essential that the TC or SR understand what security and
data integrity issues are driving the file locking requirement. Customers often include such
requirements without understanding their own environment.
HP-UX 11 CIFS/9000 / NFS File Server & Storage
Files Accessed by
Windows Clients
Files Accessed by
NFS Clients
Shared CIFS/NFS
File Access
YES – Locking Needed
No data managementNo ACLRead/WriteFilename4
NO
PDM, Clearcase, etc…No ACLRead/WriteFilename3
NO
No data managementACE on ACLRead/WriteFilename2
NO
No data managementNo ACLRead onlyFilename1
Locking Needed?Data MgtACLrwxFilename
1. Are there files or directories that will be accessed by both CIFS and NFS?
2. How many files or directories, and what kind of data?
3. Will clients have write access to the files or directories?
4. Are there ACLs on the file or directories that manage client access?
5. Is there a data management application that administers access (Clearcase or PDM server)?