Available Disk Space Low Format Pen drive In Linux

I have 4 GB Pen drive. But while I use in the Linux system it show Available Disk space 1.7 GB is Free. But I didn't use the remaining Disk Space 2.1GB .use df -h it will show the list of available Disk Space
File system Size Used Avail Use% Mounted on
/dev/sda 3.8G 2.1G 1.7G 54% /media/New Volume
So I decided to Format the pen drive

How to Format the Pen drive
Normally mkfs command is used to create the file-system.
But while we are using these command it is automatically format the pen drive. So using the mkfs we can format the Flash Drive.
[root@disk ~]# mkfs.vfat /dev/sda
mkfs.vfat 2.11 (12 Mar 2005)
mkfs.vfat: /dev/sda contains a mounted file system.

1)Unmount the pen drive
2)Delete the Partition in the Pen drive
3)using mkfs Format and Create the New File system
Unmount The Partition
[root@disk ~]#umount /mnt
Unmounted Successfully
List Out The All Partition
[root@disk ~]# fdisk -l
Here I delete the all the partition For the pen drive
Using following command
fdisk /dev/sda
d
1
2
3
d For delete.1,2,3 It will delete the partition sdb,
it will delete the all the partition in the sdb device- Flash pen drive, /dev/sdb - USB Flash Pen drive
Make The Files System.
#mkfs.ext3 /dev/sdb