Hello preethi,

this is my understanding on your question:
you need a device on which a filesystem should be created but the device should not be a mounted device.

to achieve this, you should be creating a partition using LVM or FDisk , CFDisk etc tools and format the partition using the mkfs tool with what ever file system you require.
leave this partition without mounting!!

note: creating a partition may demand for a reboot of the system in OLD versions of Linux/Unix.

-ilan