The fact is – it seems Samsung has disabled the option for some reasons (probably related to security). The device snow use MTP (Media Sharing Protocol) and PTP, which aren't very useful for everyone. For example, for Samsung Galaxy S III, instead of USB mass storage, it only features MTP, which is not as easy to use and fast, so many prefer UMS instead.
Then how to enable UMS mode for Samsung Galaxy S2, S3, Note 2 or whatever...?
Steps to Enable USB Mass Storage mode
First of all: you'll need to root your Samsung Android. Here is a step by step Android Rooting guide which you can follow for the Samsung Galaxy S2/S3 or Note 2.
For Samsung Galaxy S3
- Download the apk file here.
- Copy the apk to your device and disconnect it from your computer.
- Then install the app on your device and follow the instructions given by the app.
- Once the app is installed, you can open it and select the option you prefer for file transfer, which is very easy.
For Samsung Galaxy Note 2
- Download SGS3 Easy UMS here.
- Then you will have to launch the app, grant it root access when you're asked for it, and choose the way you want to mount your device on the PC.
- It's very easy and you will only have to tap one button to switch from one mode to another.
Note: Before starting the procedure, make sure to backup the data on your device, because there's an unlikely chance of losing it.