In addition to the EFS partition, there are several partitions on our n9005 devices that do not exist in official odin roms.
This means that they must be unique to your phone, and they might be as important to back up as the EFS folder to prevent IMEI loss or other problems (like those bootloops many people get when flashing kernels, which appear to be tied to corrupted modemst1 partitions).
These partitions are: modemst1, modemst2, fsg, fsc, backup, dbi, ddr, pad
You can see them by executing the following command:
ls -l /dev/block/platform/msm_sdcc.1/by-name/
CWM does not back up EFS at all afaik, and the EFS backup tools usually only take the EFS partition while ignoring the others.
TWRP is the only one which also backs up modemst1 and modemst2 as far as I can tell. (it creates 2 additional efs backup files with 3MB in size - which is exactly the size of these partitions.)
From further research (this was discussed in the S3 forum) it turns out that the "fsg" and the "backup" partitions are meant to take copies of the modemst1 and modemst2 partitions - this can be done/forced by executing "reboot nvbackup" in terminal or with adb. So these partitions are meant to hold the backups of modemst1 and modemst2. But I'm not sure if our devices ship with these backups already made - the S3's apparently did not, so users had to do this backup themselves. (and/or use dd to also create image backups of these partitions)
People in the S3 forum reported that when they had corrupted modemst1 and/or modemst2 partitions (and no backup available) that while they still had their imei through EFS backup (or written to the phone with qualcomm tool) that they could only use the phone on roaming with these partitions corrupted.
So does anyone actually know more about this? Please lets use this thread to figure out (and then create some sort of sticky with the info) what these partitions actually do and if they need backup.
The "bootloop" fix goes as far as formatting modemst1 and modemst2 (I done it myself too in terminal before) to fix the bootloop issue. And its said that the partitions contents are just recreated then. But from which source? EFS or the fsg / backup partitions? etc.
This really needs some further investigation I think.
What I also did was to compare all the backups I had and see if they were the same or if they did differ.... and the weird thing is that EVERY single backup I have of my EFS folder or the modemst1 and modemst2 partitions do differ in checksum and also in binary diff.
Even the EFS folder did change over the time it seems. (partially this is caused by me editing the wifi mac ... but even before I did that the efs backups did differ from backup to backup).
But nonetheless, it seems that my phone is actually working alright. I have my imei, and I can just normally log in to my carrier network (can only test hsdpa+ though) and wifi is alright too.
So it appears that modemst1 and modemst2 indeed get recreated if they are formatted, but what about those other partitions. Unfortunately (since I only have one backup of these, made by hand) I cannot compare them to see if they also changed over the time.
Last but not least: modemst1, modemst2, fsg (meant to have copy of modemst1) and backup (meant to hve copy of modemst2) also differ on my device..... (can you guys who are fit in the terminal maybe also test if the partitions differ on your phones or if they are indeed copies?)
Would really like to understand these partitions more...