What is the nature of a "MVFS filesystem" with ClearCase?

MVFS (Multi-Version Filesystem) don't so much "create" a filesystem, but give you access to one.

M: (on Windows) or /view (on Unix) is a mounting point allowing to browse the content of any Vob (the ClearCase repositories) you mount (like a classic network mount, but made by ClearCase).

When you create a dynamic view, you will use MVFS to browse the "dynamic" filesystem, meaning you want load any file on your hard disk: you will remotely see any version you have selected through the config spec of the view.

See About the MultiVersion File System (MVFS):

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.

Notes:

• a snapshot view won't use MVFS (see "What are the differences between a snapshot view and a dynamic view?")
• With a dynamic view, you can directly browse any version you want, using extended pathnames.
• Any read/write operation is done through cleartool and ClearCase: you cannot, as you tried in your previous question "rm doesn't detect failure of fchdir in walkfs", to rm elements through a Unix rm or Windows del. Only cleartool command can modify an element managed by ClearCase in a dynamic view.