Question & Answer
What information is available that provides a brief overview of the MultiVersion File System (MVFS) that is required for the use of IBM Rational ClearCase dynamic views on Microsoft Windows, UNIX and Linux?
The information below is meant to supplement the existing documentation which can be found in the IBM Rational ClearCase Information Center under the topic of The multiversion file system.
The MultiVersion File System (MVFS) creates a virtual file system specifically designed for accessing data within a Rational ClearCase VOB.
The MVFS works similarly to UNIX® Network File System (NFS), in that it loads a kernel driver that presents a file system to the user through a standard interface within the Windows, UNIX or Linux kernel.
When you start a view and mount a VOB, remote procedure calls (RPC) are made to the view to determine which cleartext files should be presented to the user.
After the MVFS gets a file name and caches it, the operating system (OS) opens a call to the underlying file system where the view or the VOB storage directory resides.
The MVFS runs in the operating system kernel and cannot be stopped or started independently of the OS. Thus, to stop and restart the MVFS on UNIX, Linux or Windows, you must shut down and restart the computer.
The MVFS extends the host’s native operating system to provide file system support for dynamic views. A dynamic view is an MVFS directory that enables dynamic access to VOB elements. Dynamic views use the MVFS to present a selected combination of local and remote files as if they were stored in the native file system.
- Rational ClearCase LT does not support MVFS.
- Both Snapshot and Web views do not use the MVFS.
Here are some distinct and similar MVFS capabilities on Windows versus UNIX or Linux.
UNIX and Linux
On any UNIX or Linux host where the MVFS is installed:
- The /view directory functions as the mount point for the MVFS namespace.
- The code that implements the MVFS is (statically or dynamically) linked with a host’s operating system, and how the MVFS is linked depends on the type and version of the operating system.
- The MVFS on UNIX and Linux is always case-sensitive; it always uses case-sensitive file look-up and does no case conversion.
- File names that include these characters are recognized by the MVFS on UNIX and Linux: ? * / \ | < >
- A UNIX or Linux host can export a view-extended path name to some VOB mount point (for example, /view/exportvu/vobs/vegaproj) to allow non-ClearCase read-only access from a host that does not have Rational ClearCase installed.
- The supported file types are Files, Directories and Symbolic links. You cannot create other file types, such as UNIX special files, within a dynamic view.
On a Windows client with MVFS installed:
- Each dynamic view appears as a share under a special network name (\\view, by default) as well as a directory under the client’s MVFS drive (drive M, by default).
- The MVFS is a file system driver that is loaded by the Service Control Manager at system start up.
- The MVFS logs error and status messages to the file C:\mvfslogs. You can use the MVFS tab in the ClearCase program in Control Panel to change this path name.
- The MVFS can be configured to support various case-sensitivity and case-preservation options since the native Windows file system is case-insensitive and case-preserving, and performs case-insensitive file look-up.
- File names that include these characters are not recognized by the MVFS on Windows (and cannot be loaded into a Windows snapshot view): ? * / \ | < >
- The supported file types are Files and Directories.
29 September 2018