You can use GParted
Install it by entering the following command in the terminal:
sudo apt-get install gparted
Here is a tutorial for formatting your USB flash drive :
How to Format a USB Drive in Ubuntu Using GParted
Select the USB drive from the top write drop-down menu.
Right click the drive and select format, then check Apply
In my laptop installed 128GB SSD and 500GB HDD and I have /, /home and swap on SSD, and store other files on HDD.
/ – 20GB;
/home – 100GB;
swap – 8GB.
All 500GB on /media/storage.
On the HDD I keep only large files that don't need high-speed read/write. It's a music, videos, ISO images, system snapshots, etc. For convenience, in my home ...
Press there and change it to /dev/sdb
About the other statement you hovering in pantheon-files and seeing less space. You have mixed concepts, remember that in Linux you have mount points acting logically as one but they are separated. What you saw as "File System" is the same amount you see in the root mount point (/). You expected to see it all together ...
I'm also facing a similar problem, and after many searches, I found these links: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1270676 and https://github.com/josch09/ampe_stor. This driver claims to support AU6601, AU6621 and AU6625. You can clone this driver and install it to see if it worked. Unfortunately, it does not work for my AU6625 card reader ...