[Samsung Galaxy Mega] starmaster10:
Hi..you are going to have to root the phone in order to do a backup..i assume your phone has knox on it already, just check my post here as you can get all 3 recoveries from it and the SuperSU zip file also, i use the TWRP recovery which can be downloaded from [MENTION=4551757]Silesh.Nair[/MENTION] signature in his post and you want to get the .tar file of which recovery you want to use as you will need a program called odin which i use 3.07 version of odin and link for odin 3.07 here and install it on your pc and put the recovery .tar file on your pc as well.

But before proceeding you have to make sure you have the samsung drivers installed on your pc so that the pc can see your device which one program is kies and can be downloaded here

Then open odin and uncheck the auto reboot box as you do not want it to reboot right away again..then you have to put the phone into download mode by first having the phone powered off and then hold the vol-down + power button until you see the samsung mega splash screen and release buttons and you will see a warning screen and then push the vol-up button and you should be now in the download mode, you will see a green android dude (but the rogers version my show a blank screen), and if the above button combo does not work do this combo then, phone powered off and then hold vol-down+home button+power button until the samsung splash screen appears and release and then just push the vol-up button to get to the download mode.

Now when you connect the phone to your pc with odin opened the first ID:COM window should light up in blue and that means your device is connected and ready to go, but make sure the auto reboot box is unchecked and now click on the PDA button in odin and find the .tar file you downloaded of the recovery and put it into the PDA window, you are now ready to flash the recovery.

Then hit the start button and odin will start flashing and it should not take long at all..when odin is finished flashing it will turn your phone off and then disconnect the phone from your pc..IMPORTANT..YOU MUST reboot the phone directly into the recovery mode otherwise the stock recovery will be put back onto the phone (this only has to be done once), you can get into the recovery mode by having phone powered off (which it should be from just flashing it) and push the vol-up+power button till you see the samsung splash screen and release, and same as above procedure if that button combo does not work add the home button in this combo also.

You should be now into the recovery mode and you will see a yellow warranty line with the blue recovery line as this is normal to see the yellow line now because of knox. then from that post download the SuperSU v1.93 zip file and put it on your sdcard or extenal sdcard if you have one in your phone and use the recovery to install it and after that you should be rooted, if you use TWRP recovery this recovery can install this part for you as it will detect it is not there and will ask if you want to install it..then you can go ahead and make a backup of your rom with the recovery..hope this will help you out and if you need more help just post. :)