The EFS holds your IMEI and other baseband-related stuff which essentially allows you to conncet to mobile networks. So if you lose your IMEI/your EFS becomes corrupt you'll find that your mobile reception won't work.
So it becomes pretty important to have a backup of it somewhere in case things go wrong (if you don't its not hard to fix, just bothersome)
Will custom rom change the values inside the efs folder if yes is it possible that we can retain the original efs values by using earlier backed efa folder
2. if the folder is created as image it is easier. Copy and paste often won't work.
Upgrading stepwise is the safest way to keep all fine (GB, ICS, JB/CM10.2, KK). Upgrading to 4.3/CM10.2 will resize the partitions so best way to downgrade again beyond 4.3 is to flash stock GB with PIT file and repartition with Odin.
Some older devices still remain very popular. Phones like theHTC Desire, Sony Ericsson … more
23 Sep 2014
By Tomek Kondrat
XDA Developers was founded by developers, for developers. It is now a valuable resource for people who want to make the most of their mobile devices, from customizing the look and feel to adding new functionality. Are you a developer?