[ZenFone 2 General] OfficerJimLahey:
TL;DR ... please skip to the bottom for a step-by-step how-to. :p

It is still a bit of a mystery on how easy it is for someone to lose their EFS data (including baseband/IMEI). It has happened a few times (judging by the forum activity). Even for more reason, especially since this data cannot be replaced without warranty work, it is always best to protect yourself.

So I took the task of backing up all my partitions (some through TWRP, others through shell/dd), and then pulling the dd'd partitions to my PC. Best practice is to back up everything...there may be something else lost that you may need in the future.

My old theory (based on grep'ping the images) targeted p16 and p18. According to /dev/block/by-name, mmcblk0p16 translates to the APD partition (which is related to the demo program), and mmcblk0p18 the system partition ...

lrwxrwxrwx root root 2015-07-07 16:40 ADF -> /dev/block/mmcblk0p17
lrwxrwxrwx root root 2015-07-07 16:40 APD -> /dev/block/mmcblk0p16
lrwxrwxrwx root root 2015-07-07 16:40 boot -> /dev/block/mmcblk0p1
lrwxrwxrwx root root 2015-07-07 16:40 boot-one-shot -> /dev/block/mmcblk0p5
lrwxrwxrwx root root 2015-07-07 16:40 cache -> /dev/block/mmcblk0p15
lrwxrwxrwx root root 2015-07-07 16:40 config -> /dev/block/mmcblk0p14
lrwxrwxrwx root root 2015-07-07 16:40 data -> /dev/block/mmcblk0p19
lrwxrwxrwx root root 2015-07-07 16:40 factory -> /dev/block/mmcblk0p12
lrwxrwxrwx root root 2015-07-07 16:40 fastboot -> /dev/block/mmcblk0p3
lrwxrwxrwx root root 2015-07-07 16:40 misc -> /dev/block/mmcblk0p13
lrwxrwxrwx root root 2015-07-07 16:40 panic -> /dev/block/mmcblk0p11
lrwxrwxrwx root root 2015-07-07 16:40 persistent -> /dev/block/mmcblk0p9
lrwxrwxrwx root root 2015-07-07 16:40 ramdump -> /dev/block/mmcblk0p6
lrwxrwxrwx root root 2015-07-07 16:40 recovery -> /dev/block/mmcblk0p2
lrwxrwxrwx root root 2015-07-07 16:40 reserved -> /dev/block/mmcblk0p10
lrwxrwxrwx root root 2015-07-07 16:40 silentlake -> /dev/block/mmcblk0p7
lrwxrwxrwx root root 2015-07-07 16:40 splashscreen -> /dev/block/mmcblk0p4
lrwxrwxrwx root root 2015-07-07 16:40 system -> /dev/block/mmcblk0p18
lrwxrwxrwx root root 2015-07-07 16:40 userkeystore -> /dev/block/mmcblk0p8

...however, the location within system is elusive (no common files between the search terms, except "/system/usr/srec/en-US/hmm_symbols", which doesn't seem to count)...

...please note, I have redacted my IMEI segments for protection.

joel@cybaryme:~/Build/ArchiKitchen-master/PROJECT_070815_181336$ grep -c -r -a abcd * | grep -v :0
system/lib/arm/libcrypto.so:1
system/lib/libstagefright.so:1
system/lib/libcrypto.so:1
system/tts/lang_pico/en-GB_kh0_sg.bin:1
system/tts/lang_pico/es-ES_zl0_sg.bin:1
system/app/ASUSBrowser/ASUSBrowser.apk:2
system/app/LiveWallpapers/LiveWallpapers.apk:1
system/priv-app/GmsCore/lib/x86/libsslwrapper_jni.so:1
system/priv-app/FileManager2/x86/FileManager2.odex:1
system/priv-app/AsusZenUIServices/x86/AsusZenUIServices.odex:1
system/usr/icu/icudt53l.dat:1
system/usr/srec/en-US/hmm_symbols:1
system/usr/xt9/databases/ldb/ZHsbUNps_GB18030_xt9_big.ldb:1
system/bin/wpa_supplicant:1
system/bin/hostapd:1

joel@cybaryme:~/Build/ArchiKitchen-master/PROJECT_070815_181336$ grep -c -r -a efgh * | grep -v :0
system/etc/security/cacerts/ccc52f49.0:1
system/etc/catalog/V1_7260/audiocomms_config/parameter-framework/Settings/Audio/AudioConfigurableDomains.xml:35
system/etc/catalog/V1_DSDA/audiocomms_config/parameter-framework/Settings/Audio/AudioConfigurableDomains.xml:29
system/framework/x86/boot.oat:1
system/usr/srec/en-US/hmm_symbols:1
system/usr/xt9/databases/ldb/ENubUN_xt9.ldb:1
system/usr/xt9/databases/ldb/ESusUN_xt9.ldb:1
system/vendor/lib/libWVStreamControlAPI_L1.so:1

joel@cybaryme:~/Build/ArchiKitchen-master/PROJECT_070815_181336$ grep -c -r -a ijkl * | grep -v :0
system/etc/security/cacerts/d16a5865.0:2
system/tts/lang_pico/en-GB_kh0_sg.bin:1
system/app/MYuppyHK_Medium/MYuppyHK_Medium.apk:6
system/app/YouTube/YouTube.apk:1
system/app/Newsstand/x86/Newsstand.odex:1
system/usr/srec/en-US/hmm_symbols:1
system/usr/xt9/databases/ldb/ITusUN_xt9.ldb:1

joel@cybaryme:~/Build/ArchiKitchen-master/PROJECT_070815_181336$

Just recently, user noviardi did a real world test with two devices...one with a working baseband, the other with a borked EFS. Noviardi managed to get device number two working by cloning p14 (also known as the config partition). Please note there are consequences, that with this solution, only one device can be "online" at a time, or the functioning IMEI will get blacklisted (then neither devices will have cell access). Which is the least of the problems. Hence, why I do not share my EFS data (neither should anyone else), or even snippets.

So, if you want to back up your EFS for personal resuce, your best shot is to back up the mmcblk0p14 / Config partition. But if you are paranoid (like me :)), might as well back up everything. :cowboy:

Here's how to do it:

Connect the device to your PC

Turn on USB debugging (if not already)

From your PC, fire up a terminal/command prompt

Type "adb shell" (without the quotes - may need to add "sudo" to the front depending on your situation)

Run these commands:

su
dd if=/dev/block/mmcblk0p14 of=/storage/MicroSD/mmcblk0p14.img

Repeat the last line for any other partitions to back up (changing both numbers)

Type "exit", press enter (and repeat to close adb shell)

Run the following command:

adb pull /storage/MicroSD/mmcblk0p14.img .

Repeat for any other partitions to copy to your PC

Close out terminal, unplug USB cable.

Also, there is at least one version of TWRP (TheSSJ's release) that will back up your Config partition for you, as Config is also responsible for connectivity issues (not related to IMEI) switching between ROM's.

Hope this helps on how to protect your IMEI, with a big thanks to noviardi.