How to backup the data partition

/!\ Warning: Draft

This article is in draft form and is being written:

Also a big part of this article is copied from BackupTheEFS, it would be better to find a way to include content instead.

What does the data partition contains?

It probably depends on the devices and the Android versions.

On Replicant 6.0, it contains at least the application internal data: When various applications are installed, they have access to some storage where they can read and write data that is only visible to them and not to other applications. This is part of the Android security model that doesn't trust applications even if they are fully free software.

In addition, on some devices it also contains the users data. This location and external microSD cards is where users typically their files like Music, photos, etc. This data is made accessible to the users in various location through a mechanism called fuse. In Replicant 6, this data is stored in the media directory in the data partition.

Summarry:
Mount points Content
/data/ Applications (internal) data
/sdcard
/storage/<UUID> 		User accessible storage to store music, photos, etc

Here's where the sdcard user accessible storage comes from:

/sdcard -> /storage/self/primary [1]
/storage/self/primary -> /mnt/user/0/primary [2]
/mnt/user/0/primary -> /storage/emulated/0 [3]

1 

root@i9300:/ # readlink /sdcard                                                                                                                            
/mnt/user/0/primary

2 

root@i9300:/ # readlink /storage/self/primary                                                                                                              
/mnt/user/0/primary

3 

root@i9300:/ # readlink /mnt/user/0/primary                                                                                                                  
/storage/emulated/0

4 

root@i9300:/ # mount | grep "/storage/emulated"                                                                                                              
/dev/fuse on /storage/emulated type fuse (rw,nosuid,nodev,noexec,noatime,user_id=1023,group_id=1023,default_permissions,allow_other)

TODO:

Concerns about the application internal data

TODO:

Howto

TODO:

Galaxy S III (GY-I9300)

First, you need to make sure that the data partition is not mounted.

To do that, you can run this command:

adb shell "umount -l /data"

If the /data partition was mounted, it will unmount it. This will look like that:

$ adb shell "umount -l /data" 
$

If it was not mounted, it will instead show an error that we can ignore:

$ adb shell "umount -l /data" 
umount: /data: Invalid argument

Once this is taken care of, we can backup the partition with the following command:

adb pull /dev/block/platform/dw_mmc/by-name/USERDATA ./

See also