You can ignore this article if you did not root Samsung Galaxy S III. Why? Because you need root access to backup and restore Samsung Galaxy S3 EFS. And you don’t need to worry about EFS at all when not rooted.
What is EFS? It is a place that stores your Android smartphone important data like Wi-Fi, Bluetooth MAC address and IMEI (nv_data.bin). Do take note if you are a frequent ROM / firmware flasher or rooted your Android phone. Installed unstable poorly cooked ROM might cause EFS partition to be corrupted or missing. Which will make your Samsung Galaxy S3 fail to make voice call due to missing IMEI number. So better to make a backup of your Samsung Galaxy S3 EFS partition.
The easiest way to backup EFS ~ use EFS backup / restore tool like kTool by Hellcat. kTool will backup the whole EFS partition (including files read / write permission) for you with 1 click. And do verify EFS Backup after that. kTool will generate 2 files ~ efs.img and efs.tar.gz on sdcard. Make sure to keep another copy on PC or cloud storage.
Download HC-kTool at Google Play Store here.