What is the difference between EFS and persist partition ?

[osemoka]

Hey. Can anybody tell me the difference between those two ? I know it's recommended to backup them before os migration. I read that both of them stores information about imei, mac etc. Do I need both of them to safely migrate to new os'es?

 

[NZedPred]

The short of it is that your Persist holds the key files needed to create your IMEI, and it is used to construct your EFS. EFS effectively works as a cache. If you wipe EFS, then as long as you have an intact Persist, your EFS will be reconstructed, and you will keep your IMEI.

Credits to this thread for working out the relationship between Persist and IMEI (it is talking about the investigation into how to restore IMEI when it is 0 after flashing Oreo custom roms):
https://forum.xda-developers.com/g5-plus/how-to/dev-fixing-baseband-t3806064

Even though it is for potter (G5 Plus), it still applies to Sanders.

 

[5P4RT0N]

doubt

The short of it is that your Persist holds the key files needed to create your IMEI, and it is used to construct your EFS. EFS effectively works as a cache. If you wipe EFS, then as long as you have an intact Persist, your EFS will be reconstructed, and you will keep your IMEI.

Credits to this thread for working out the relationship between Persist and IMEI (it is talking about the investigation into how to restore IMEI when it is 0 after flashing Oreo custom roms):
https://forum.xda-developers.com/g5-plus/how-to/dev-fixing-baseband-t3806064

Even though it is for potter (G5 Plus), it still applies to Sanders.

if i have someone else persist the imei not reconstructing with their value why...??
they are keeping some values somewhere else ...

 

[NZedPred]

if i have someone else persist the imei not reconstructing with their value why...??
they are keeping some values somewhere else ...

The files that store the information, dhob.bin,etc, are encrypted and can only be decrypted by the device they were made for.

 

[osemoka]

So my question is : Persist is just a 2nd safety measure, which can help if we loose EF? So can I do those backups from custom softs and there will be no difference if i did it from official soft? My imei's are not lost.

Edit 1
I backed up persist with TWRP from this topic https://forum.xda-developers.com/moto-g5s-plus/help/how-to-persist-partion-moto-g5s-t3830442
How do I know if its allright ?

 

[NZedPred]

So my question is : Persist is just a 2nd safety measure, which can help if we loose EF? So can I do those backups from custom softs and there will be no difference if i did it from official soft? My imei's are not lost.

There's a little bit more to it than that. OTAs normally wipe the EFS on install, so it's not that persist is a safety measure, it is the primary means of getting your IMEI. Additionally, there are certain folders that are used when using things like 4G, Volte, etc. A number of other things get stored there, such as files for widevine (DRM), calibration for sensors, etc. That's why it is so important.

Edit 1
I backed up persist with TWRP from this topic https://forum.xda-developers.com/moto-g5s-plus/help/how-to-persist-partion-moto-g5s-t3830442
How do I know if its allright ?

I can't tell what that specific version of TWRP does to backup persist, but if it's done as an image it will be about 32MB, or if it's done as 'files only' it will be around 3-400KB.