Hello and welcome to the forum,
What is MVS?
The most-used (counting numerous upgrades) operating system on an IBM mainframe.
can u given an clear idea regarding this in mainframe environment...
Probably not. The forum is not the place for such an encompassing question. For one definition, you could look at wikipedia.
how the data in is stored in mvs...
Too many ways to go into here. Not only are there many "ways" to store data, there is also different kinds of media. These are not "hot-switchable" like usb devices on the pc.
What is it you really want to know?