Hello all, I'd like to talk about a popular topic generally considered to be relevant to rooted Samsung Android devices. Why do I want to talk about this particular topic? Well because I think people should know, as I feel not enough people know about it.
The topic in question is about the /EFS folder which is a hidden folder in the core of your Samsung Android device. Why is this folder important? Well it's important because this particular folder stores your unique identification files, such as your devices IMEI number, MAC addresses for the radios, ESN numbers, etc. You get the jist.
If you have rooted your Samsung device, PLEASE, back this folder up. This folder is incredibly valuable to the functioning of the phone. If this folder becomes corrupt when flashing ROMs, or installing new recoveries, then your phone turns into an expensive paperweight.
How do I know this? Well, in an unfortunate chain of events, I have had the "joy" of experiencing this. Without a backup of my /EFS folder, my phone, Samsung Galaxy S3, is now a VERY expensive paperweight.
Had I known before about the /EFS folder, I would've backed-up. However I didn't, and as things go, I'm now left without a phone... for now.
I urge you all to back up your /EFS folder. There are many tools on XDA-Developers that can help with this, however you can with Android Terminal Emulator run:
busybox tar -cv -f efs.tar -C /sdcard /efs
Ensure you have Busybox installed when doing this (though you should have busybox installed anyway.)
I hope people can learn from my mistake.