Database Users

SDcard Filesystem

I (along with other people) find it weird that Asus chose to mount the sdcard to /Removable/MicroSD instead of the traditional /mnt/sdcard.
I would like Titanium Backup to store the files on my sdcard instead of the internal memory, but the problem is that TI only checks the /mnt/sdcard directory. So in my infinite geek knowledge I had the idea to symlink /Removable/MicroSD/TitaniumBackup to /mnt/sdcard/TitaniumBackup. The problem is that FAT32 doesn't support symlinks, so I formatted the sdcard to NTFS and popped it back in but it wouldn't mount it, which I realized was because it doesn't have the NTFS modules. So I popped it back out and formatted it as ext2, but it still wouldn't mount automatically and I couldn't mount it manually because I didn't know what the device name was.
Anyone have any solutions?

You can try ask the developer of TitaniumBackup to include support for asus TF.

Obviously I already did that but I'm looking for a fix on my end.

As with most other tablets, the internal SD is mounted to mnt/sdcard so external SD has to be mounted elsewhere.
As far as TB goes, you can choose where to store backups. Have currently got it setup to backup to Removable/MicroSD/TitaniumBackup
EDIT: If you go into TB preferences menu, scroll down to Backup folder location, then press the Back icon (the system one) to get back to the root folder. Then you can choose the Removable/MicroSD/ folder. Click on "create a new folder", call it what you want, then open that folder. Click the "Use current folder" button and there you go...Backup folder on external SD!
Took me a while to realise that the back icon took you back up the folder tree, rather than closing the folder location window!

It would be nice if we could get a custom mount script or something that would mount the sdcard to something like /mnt/sdcard/music. I'd love to have my music synced to card and everything else stored internally...

fisha21 said:
EDIT: If you go into TB preferences menu, scroll down to Backup folder location, then press the Back icon (the system one) to get back to the root folder. Then you can choose the Removable/MicroSD/ folder. Click on "create a new folder", call it what you want, then open that folder. Click the "Use current folder" button and there you go...Backup folder on external SD!
Took me a while to realise that the back icon took you back up the folder tree, rather than closing the folder location window!
Click to expand...
Click to collapse
Thanks! Thats what I needed to know, I was thinking its kind of stupid that they only have a "detect" button.

brando56894 said:
I (along with other people) find it weird that Asus chose to mount the sdcard to /Removable/MicroSD instead of the traditional /mnt/sdcard.
I would like Titanium Backup to store the files on my sdcard instead of the internal memory, but the problem is that TI only checks the /mnt/sdcard directory. So in my infinite geek knowledge I had the idea to symlink /Removable/MicroSD/TitaniumBackup to /mnt/sdcard/TitaniumBackup. The problem is that FAT32 doesn't support symlinks, so I formatted the sdcard to NTFS and popped it back in but it wouldn't mount it, which I realized was because it doesn't have the NTFS modules. So I popped it back out and formatted it as ext2, but it still wouldn't mount automatically and I couldn't mount it manually because I didn't know what the device name was.
Anyone have any solutions?
Click to expand...
Click to collapse
What? You're doing it backwards!
If TI is writing to /mnt/sdcard/TitaniumBackup, but you want it to write to /Removable/MicroSD/TitaniumBackup instead, then /mnt/sdcard/TitaniumBackup should be the symlink, pointing to a directory on the SD card!
The target's filesystem doesn't matter (fat32), only the source's (i.e. ext4 on the internal storage).

Good catch, either way it doesn't matter now because I don't need symlinks since I know how to do it in TB now.

CWM nandroid backup backs up internal SD also?

hi, when I goto android recovery mode
there are some options in how to create backups
I usally go for the full one including the webtop partition.
now my question is there are 2 storage location
internal sd and external sd
where android store its applications and music and so on
if i back up fully including the webtop,
will internal SD card also backed up?
if not what would be the best practice to backup the internal SD card (they store application data)
what I usually do after updating to a new rom is
clear cash hardreset dalvik cache, and finally format the internal SD card
thank you in advance.

leegoon84 said:
hi, when I goto android recovery mode
there are some options in how to create backups
I usally go for the full one including the webtop partition.
now my question is there are 2 storage location
internal sd and external sd
where android store its applications and music and so on
if i back up fully including the webtop,
will internal SD card also backed up?
if not what would be the best practice to backup the internal SD card (they store application data)
what I usually do after updating to a new rom is
clear cash hardreset dalvik cache, and finally format the internal SD card
thank you in advance.
Click to expand...
Click to collapse
no, CWM/nandroid does NOT back up your sdcard. to back up your SDCard, you should copy it over to your computer. but there is no reason to have to back it up every time you do a rom flash
there is no reason for you to format your internal SD card either
also, i think your steps for flashing a new rom are a little backwards.
typically a rom will wipe your dalvik cache for you (not always, but most of the time)
clearing cache and hardreset should be done BEFORE you flash a rom. a hard reset (formats /data in the process) will remove any /data that the rom dev may have put in...

Pirateghost said:
to back up your SDCard, you should copy it over to your computer.
Click to expand...
Click to collapse
You can also copy the internal sd card to your external sd card.
If you do it manually with adb over romracer's CWM, you have to mount the right partitions. You can do this with the CWM mount menu or with the following commands:
Code:
mount /emmc
mount /sdcard
After mounting you can copy:
Code:
copy -R /emmc /sdcard/internal_sdcard_backup

3dik said:
You can also copy the internal sd card to your external sd card.
If you do it manually with adb over romracer's CWM, you have to mount the right partitions. You can do this with the CWM mount menu or with the following commands:
Code:
mount /emmc
mount /sdcard
After mounting you can copy:
Code:
copy -R /emmc /sdcard/internal_sdcard_backup
Click to expand...
Click to collapse
WOW.
way to necro a 3 year old thread

Why not? My post could still be useful for some users.

3dik said:
Why not? My post could still be useful for some users.
Click to expand...
Click to collapse
Yes, its very smart to ressurect a dead thread that's nearly 4 yrs old. Its not like your input is already known and used in the 4 yrs since the last post, but then again you're like the Korean user who recently gave directions on how to install CM7. Stating obvious facts that everyone or at least most ppl already know.
Sent from my ATRIX HD using XDA Free mobile app

Let's google: atrix 4g backup internal sdcard
The first entries say the same as Pirateghost says: copy internal sdcard to the computer. Ok, this is already known.
I explained the external sdcard way because I have problems pulling big files via ADB. I'm sure I'm not the only one. I know XDA is not Stackoverflow, but OP asked for the best method for backing up internal storage. And copying to external sdcard is the best method imho.
But let's assume that your device is broken and you're restricted to the use of CWM. The CWM mount points differs from the moint points of the Atrix Android. Are the details common knownledge? I found the mount point descriptions at the changelog and at page 56(!) of romracers CWM thread..
My post is like a summary of my research. I it reduces the research time for other users. Tell me a better place to contribute that knowledge than this thread.

Guys, yes, he has brought a dead thread back, it's not always the best thing to do, but what's even worse is trying to argue about it. If you don't agree with the person reviving an old thread, then just report it and let us mods take care of it. Don't go out telling people they might have screwed up, especially when it's no big deal like this one...
So I'll leave it at that now

[How To] Swap the mounting points on ICS (CM9) for emmc and sdcard.

This is a quick tutorial I want to write up based on a recent experience I've had recently with my micro sd-card. (More info on that below)
This how to shows how to switch between the internal sd card and the external sd cards mounting points (so the external is accessed via /sdcard, and the internal is accessed through /eemc)
The nuts and bolts how to:
0. Perform backups on System, i am not responsible for any damages or boot loops.
1. Download root explorer (or any other file explorer with root privileges)
2. Go to /system/etc, and mount R/W
3. Long press on vold.fstab and select Open With... , select Text Editor
4. You will find a line with sdcard in it a few times, change this section:
dev_mount sdcard /mnt/sdcard
Click to expand...
Click to collapse
To:
dev_mount emmc /mnt/emmc
Click to expand...
Click to collapse
5. Do the same thing with the emmc section:
dev_mount emmc /mnt/emmc
Click to expand...
Click to collapse
To:
dev_mount sdcard /mnt/sdcard
Click to expand...
Click to collapse
6. But you just flipped the first section around? Yes I did, this changes the mounting points. But not the original location of where it is being mounted......
7. Please don't change anything else in this file....
8. Reboot, enjoy!
I had to do this hax because the current nightly of CM9 doesn't support there being no external sd card, and mine got corrupt (eep!), it then continued to mount the internal sd card location to emmc instead (wtf?). So i did this quick hax so i could take pictures with the stock camera and use several applications which just default to the internal sdcard (and doesn't allow changing that).
Hope that helps some random Googlers......
Note: This has only been tested on CM9 Nightly apr-9th on SGSII, but i see no reason for this not work across all ROMs and devices( with ICS, the emmc thing wasn't on GB and below i don't think) as long as you don't do anything as foolish as change more than the lines specified above.
An example of a swapped file is (DO NOT COPY AND PASTE THIS, YOU PROBABLY WONT BE ABLE TO BOOT):
# internal sdcard
dev_mount emmc /mnt/emmc 11 /devices/platform/dw_mmc/mmc_host/mmc0/mmc0 encryptable_
# external sdcard
dev_mount sdcard /mnt/sdcard auto /devices/platform/s3c-sdhci.2/mmc_host/mmc1
Click to expand...
Click to collapse
Please note that the latest CM9 nightlies lets you do this from the system menu! This was written pre that advancement. This is for the curious and other ROMs/phones.

Is it possible to use something in the lines of:
dev_mount emmc /mnt/external_sd ? To just bind the external sd to the stock location?

If I understood your question right, that's the default behavior in CM7/9 so you don't need to change anything.
(internal gets mounted as /sdcard and external as /emmc. At least that's how it always behaved on my device -takes a bit of getting used to but it's manageable once you know the trick)
edit : aw sawry, mistook /mnt/external_sd for /mnt/sdcard. But it changes nothing besides the name of the mountpoint, easily adjustable.. Although why you would want to have it named like that is beyond me, it makes for more keys to hit when typing it... xD

Zewsan said:
Is it possible to use something in the lines of:
dev_mount emmc /mnt/external_sd ? To just bind the external sd to the stock location?
Click to expand...
Click to collapse
same doubt raised here ...is it possible to mount external sdcard to /mnt/external_sd instead of mnt/emmc...???
please need solution

Zewsan said:
Is it possible to use something in the lines of:
dev_mount emmc /mnt/external_sd ? To just bind the external sd to the stock location?
Click to expand...
Click to collapse
Its the same technique....
So remember this:
Format: dev_mount <label> <mount_point> <part> <sysfs_path1...>
Click to expand...
Click to collapse
So <label> doesn't really matter, but we may as well keep it sane (and have it the same name as the mount point)! And <mount_point> is where its mounted. Make sure the folder exists first though! leave <part> and <sysfs_path*> alone and it will work correctly.
So if you were to create a folder /mnt/hammertime , then make a line look something like this (taken from my example in first post)
dev_mount hammertime /mnt/hammertime auto /devices/platform/s3c-sdhci.2/mmc_host/mmc1
Click to expand...
Click to collapse
That will work correctly.
Hope that helps!

mattisdada said:
Its the same technique....
So remember this:
So <label> doesn't really matter, but we may as well keep it sane (and have it the same name as the mount point)! And <mount_point> is where its mounted. Make sure the folder exists first though! leave <part> and <sysfs_path*> alone and it will work correctly.
So if you were to create a folder /mnt/hammertime , then make a line look something like this (taken from my example in first post)
That will work correctly.
Hope that helps!
Click to expand...
Click to collapse
is there no any requirement of changing build.prop file after doing this....?????

Ok I'll bite, late night tonight I'm going to flash back to AOKP....and give it a shot. It can't be that simple.....
Most certainly appreciate your effort...been looking for this for some time now.l!

HAvoktek said:
Ok I'll bite, late night tonight I'm going to flash back to AOKP....and give it a shot. It can't be that simple.....
Most certainly appreciate your effort...been looking for this for some time now.l!
Click to expand...
Click to collapse
I didn't think so either, but i had the problem, hoped it was like its Linux cousin and searched for fstab, i found it. Swapped the mounting destinations around. And voila, done.....

Swapped but CWM Recovery still the same
Hi, first of all nice guide you did here.
Here's the thing: somehow somewhere by flashing nightlies i ended up
with /sdcard being treated as my external SD while /emmc was for internal.
So I wanted to fix that and using your guide although the other way around
I was able to make it as such: /sdcard = internal storage; /emmc = external storage.
ALL IS GOOD however when i booted to CWM recovery:
CWM still mounts my internal storage as /emmc.
SO in recovery internal storage = /emmc while when in CM9 internal storage = /sdcard
Is there anyway i can change CWM so that internal storage = /sdcard? to be more uniform and not confusing

jeromepaez said:
Hi, first of all nice guide you did here.
Here's the thing: somehow somewhere by flashing nightlies i ended up
with /sdcard being treated as my external SD while /emmc was for internal.
So I wanted to fix that and using your guide although the other way around
I was able to make it as such: /sdcard = internal storage; /emmc = external storage.
ALL IS GOOD however when i booted to CWM recovery:
CWM still mounts my internal storage as /emmc.
SO in recovery internal storage = /emmc while when in CM9 internal storage = /sdcard
Is there anyway i can change CWM so that internal storage = /sdcard? to be more uniform and not confusing
Click to expand...
Click to collapse
Yeah CWM doesn't read the /system stuff, it has its own partition....
I've got no idea sorry, but its just a little inconvenient in CWM thats all.... But im sure you can check it out... Just search for fstab when you figure out how to explore the recovery partition (I've got no idea , short of modifying a flashable zip first and rekeying it.)

Forgot to post back with my results, Got HFS & AOKP to see the changes, however something broke when I did a PC mount. After playing with the lines "Experimentation" if you will, I ended up needing to rebuild my partitions! No fault of yours, I just wanted to see if I can have that functionality through the whole phones usage and features eg. mounting to the PC.
Thanks for the guide though, I'm seeing now that some devs are including the option to use the internal memory via a menu select, I wonder how there implementing that.

Probably something very similar but programmatically instead of the haxy file editing method I'm noting to use .
PC mounting is working as per normal for me here though...... (I don't have an external card right now so that may be a variable)

mattisdada said:
Probably something very similar but programmatically instead of the haxy file editing method I'm noting to use .
PC mounting is working as per normal for me here though...... (I don't have an external card right now so that may be a variable)
Click to expand...
Click to collapse
That it is, cause I can see my internal, but it doesn't mount the external.

Purpose
What is the purpose of this? Does it mount the EMMC so that the system thinks EMMC is actually an external sd card?
I am trying to figure out if there is a way to make the above mentioned happen. Or is there a way to re-partition it so that EMMC is used as system memory... or maybe even both? It seems that since ICS better integrates with on board memory, there would be a way to better integrate the internal memory of older devices with the system.

hfj00788 said:
What is the purpose of this? Does it mount the EMMC so that the system thinks EMMC is actually an external sd card?
I am trying to figure out if there is a way to make the above mentioned happen. Or is there a way to re-partition it so that EMMC is used as system memory... or maybe even both? It seems that since ICS better integrates with on board memory, there would be a way to better integrate the internal memory of older devices with the system.
Click to expand...
Click to collapse
This guide shows you how to "flip" the points. Several ROMs have it differently preconfigured. But if this is your current situation:
Code:
Emmc: External SD Card
SDcard: Internal SD Card
It will make it:
Code:
Emmc: Internal SD Card
SDcard: External SD Card
And vice versa obviously (its a flip).
This guide will do what your wishing it to do.
The folders sdcard and emmc (or there /mnt varient more closely) are just soft links, meaning they don't really exist, but just point to another location. We can modify which folder they are linked to in the fstab.void file.

so to make emmc to external_sd i change "dev_mount emmc /mnt/external_sd"?

Worked great on a Captivate running AOKP-36 right after a wipe data/factory.

lol you need no guide on cm9
you can switch them in storage settings by a simple checkbox
its mentioned in team hacksung's FAQ

Im on CM9. Can someone post the code so i can just do a simple copy and paste? I wanna switch emmc to external_sd
(there is no storage settings simple checkbox for me)
Sent from my SGH-I997 using xda premium

bradman117 said:
Im on CM9. Can someone post the code so i can just do a simple copy and paste? I wanna switch emmc to external_sd
(there is no storage settings simple checkbox for me)
Sent from my SGH-I997 using xda premium
Click to expand...
Click to collapse
Never use a copy and paste for the file in this operation. You only need to modify partially two lines (which you can copy and paste from the OP).
Your just swapping two words around really. Its fairly easy, just follow the steps and it will work, it looks daunting at first if your not used to doing this sort of thing, but its fairly easy.

IDEA: Hacking internal/external sdcard mount paths

Hello.
I'm using the latest aurora and I'd like to discuss an idea I had.
Since the U8800 has plenty internal memory and it's quite fast comparing to an average sd card, it'd be great if we could use the internal memory for the tasks that need "speed" instead of "space".
Running apps from the sd card is the perfect example!
So the idea would be, while keeping the external sdcard mounted on /mnt/sdcard, having /mnt/sdcard/Android/data, for instance, point to the «internal sdcard path»/Android/data.
What do you think would be the best solution:
- hacking the mount points?
- using links?
- other solution?
Any developer or filesystem savvy user can point the advantages or dangers of using this solution?
- e.g.: the system or some apps may check if the external sd-card is mounted before trying to read/write to /mnt/sdcard/Android/data... that would mean the system/those apss may think that path isn't reachable with the ext-sdcard unmounted, altough they can be read.
Suggestions? Rants? Ideas?
Regards!

I have wondered if the /data/app or maybe the whole /data partition could be mounted in the internal storage partition. That would give 2gb space for apps and associated files instead of 3-400 ish and would mean no need to move apps to sd card which would mean faster loads at startup due to internal memory being faster.

VuDuCuRSe said:
Hello.
I'm using the latest aurora and I'd like to discuss an idea I had.
Since the U8800 has plenty internal memory and it's quite fast comparing to an average sd card, it'd be great if we could use the internal memory for the tasks that need "speed" instead of "space".
Running apps from the sd card is the perfect example!
So the idea would be, while keeping the external sdcard mounted on /mnt/sdcard, having /mnt/sdcard/Android/data, for instance, point to the «internal sdcard path»/Android/data.
What do you think would be the best solution:
- hacking the mount points?
- using links?
- other solution?
Any developer or filesystem savvy user can point the advantages or dangers of using this solution?
- e.g.: the system or some apps may check if the external sd-card is mounted before trying to read/write to /mnt/sdcard/Android/data... that would mean the system/those apss may think that path isn't reachable with the ext-sdcard unmounted, altough they can be read.
Suggestions? Rants? Ideas?
Regards!
Click to expand...
Click to collapse
Well this is known for a while now . Quoted from my thread here:
vold.fstab - CHANGE THE DEFAULT SDCARD: -thanks to julle131
There is this file named vold.fstab at your /system/etc/ folder, which controls which of your sdcards (Internal/External) will be mounted when you connect your phone to the PC. The last 2 lines are the only that matter. These are the two possibilities:
EXTERNAL SDCARD MOUNTED (DEFAULT):
dev_mount sdcard /mnt/sdcard auto /devices/platform/msm_sdcc.4/mmc_host
dev_mount emmc /mnt/sdcard1 14 /devices/platform/msm_sdcc.2/mmc_host
INTERNAL SDCARD MOUNTED:
dev_mount sdcard /mnt/sdcard 14 /devices/platform/msm_sdcc.2/mmc_host
dev_mount emmc /mnt/sdcard1 auto /devices/platform/msm_sdcc.4/mmc_host
change them as you wish with a root explorer or before flashing.
Click to expand...
Click to collapse
Make this change and every app will use the internal sdcard. Gallery works ok with images to external sdcard, it just might take a while for the first refresh. But I don't know if you'll notice any difference in terms of speed....
Cheers

spirosbond said:
Well this is known for a while now . Quoted from my thread here:
Make this change and every app will use the internal sdcard. Gallery works ok with images to external sdcard, it just might take a while for the first refresh. But I don't know if you'll notice any difference in terms of speed....
Cheers
Click to expand...
Click to collapse
That's not what he talked, I think. He said that the apparel would be installed on the external sd card, but the data would be moved to the internal one. And we have speed, but the main card would be the external one.
I think its a great idea if I understood it right!
Sent from my U8800 using xda premium

mrasquinho said:
That's not what he talked, I think. He said that the apparel would be installed on the external sd card, but the data would be moved to the internal one. And we have speed, but the main card would be the external one.
I think its a great idea if I understood it right!
Sent from my U8800 using xda premium
Click to expand...
Click to collapse
Oh I see! Sorry about that. As far as I know apps are not choosing were to put their data. They just say to the OS "I want these things to be at the sdcard" and the OS puts them at the correct place. So you can't "hack" the app to "see" at somewhere else. On the other hand the OS initialises on boot which card is the primary and which is the secondary. So my knowledge stops there and I can't imagine a way to make this separation between app data and the rest...
I hope for someone else's help!

PaulMilbank said:
I have wondered if the /data/app or maybe the whole /data partition could be mounted in the internal storage partition. That would give 2gb space for apps and associated files instead of 3-400 ish and would mean no need to move apps to sd card which would mean faster loads at startup due to internal memory being faster.
Click to expand...
Click to collapse
Maybe this cannot be done, because I think that the mapping of the partitions and mounts comes from the bootloader, but there is already the solution of resizing the data partition using the space of internal storage.

PaulMilbank said:
I have wondered if the /data/app or maybe the whole /data partition could be mounted in the internal storage partition. That would give 2gb space for apps and associated files instead of 3-400 ish and would mean no need to move apps to sd card which would mean faster loads at startup due to internal memory being faster.
Click to expand...
Click to collapse
That's a great idea!
I almost don't use the so called "internal sd card", therefor I have 2GB of fast empty space being wasted.
Why not simply mounting the internal sd-card partition in the data folder and the data partition on the internal sd card folder?
I only use the internal sd card to hold ringtones and other small stuff that I need to be in accessible 100% of the time, so a few hundred MB are enough!
Me gusta!
Every ROM flashes it's own fstab, right?
So all we'd need to do would be, editing the fstab before flashing it.
-----------------
Regarding the my first idea... I don't think one can simply mount a path on another path. We'd need a "virtual" device pointing to /mnt/sdcard-internal/data/ then mount that virtual device on /mnt/sdcard-external/data/.
My knowledge of unix mount/filesystems is not much more than what's explained here: https://help.ubuntu.com/community/Mount
OK, just found this:
http://askubuntu.com/questions/11079/mount-a-directory-to-look-like-a-drive
there is a FUSE filesystem named bindfs that probably does exactly what you want. For example the following:
bindfs -n /media/USB-HDD-01/ISO/ /home/johnc/ISO-images
Click to expand...
Click to collapse
would result in ISO-images to show up as a mounted filesystem in the Places sidepanel in Nautilus. The -n is required because otherwise bindfs tries to use the allow_other FUSE option, which by default is not allowed for regular users (if you use bindfs in /etc/fstab this is not a problem).
The first directory you give is the existing one, the second directory you give is an empty directory under which the contents of the existing one will appear.
Click to expand...
Click to collapse
So, bindfs depends on FUSE... and there's a port of fuse to android: https://github.com/seth-hg/fuse-android but looking at the README I get the feeling that it's not really working. The last step would be having a kernel with FUSE support... and regarding that, I have no idea, how easy it is to get a kernel like that for our U8800 :\

Finding such a solution to expand the DATA partition indirectly would be great!
I used to apply genokolar's custom partition method as "1.2G DATA + 1.46G INTERNAL SD" before, but i found out that it has some issues with Official 2.3 Roms. One of them -the most important IMHO- is the BOOTLOOP problem occurring in some specific situations!!!
See the details in my post here:
http://forum.xda-developers.com/showpost.php?p=25853141&postcount=134
(Seems that I don't encounter the bootloops on Custom Roms, but i'm not %100 sure and never will be )
So i unfortunately gave up using it, and revert to the stock partition .
I will be grateful to the one who will find a better and reliable solution. Hope to see it soon...

I still have to gather more information on the official update "modus operandi".
My goal is to simply reformat both partitions and then swap their mount points.
If the official update formats the partitions before applying the flashing official ROM files, then partitioning changes shouldn't cause any failure on the official update.
But like I said, I'm still yet to confirm that info.
Gen's idea was great (I learned a lot just by looking at his scripts) but resizing partitions has its dangers.
Since "no one" really uses the internal memory, why not simply exchange its room with /data, right?

This would be awesome! I would love to have 2gb for apps, instead of cluttering my phone.. plus the 2gb of internal storage are just a waste for me.. I never use them.. so this would be great!

[A] Regarding Mounting SD Card in TWRP

After a few days of googling, i stumbled upon a thread in Droid DNA forum. Which led me to this answer right from the source on why it's not possible to mount our SD Card or actually, just a folder in /data, in TWRP.
Just wanted to share and hope this will clear things up and hoping that people won't wipe their /data partition since it will delete the SD Card folder as well.
I find this very enlightening so read on.
What is a data media device?
I'm writing this page because there seems to be a lot of confusion about how many of the newer Android devices work. Starting in Honeycomb 3.0 with the Xoom, Google changed the way that they handled storage. Instead of having a "data" partition with your apps and a separate "sdcard" partition for storage, Google started giving you a single, very large data partition. Inside /data is a folder at /data/media that contains all of the contents of what you think of as your internal sdcard.
Since /data/media is part of /data, we pretty much never actually format the data partition. Formatting data, of course, also removes the media folder that contains the internal sdcard. When you choose a factory reset, instead of formatting, we use rm -rf commands to remove all the folders except for the media folder so that we can remove all of your apps and settings while leaving your "sdcard" intact. In TWRP we also have a wipe internal storage option that rm -rf's the media folder and a "Format Data" option that formats to recreate the entire file system in case something goes completely wrong or to remove device encryption.
When you're booted to Android, Android fuses the media folder to /sdcard and emulates a FAT files system that doesn't have permissions for legacy apps. We don't currently have fuse in recovery, so we just add an extra mount command to mount /data/media to /sdcard so in recovery you still have to worry about permissions on /sdcard.
Because the "internal sdcard" is not a true FAT file system, you can't mount it via USB storage. Well, that's not technically true, but the vast majority of people use Windows computers and Windows doesn't recognize ext4. If we were to allow you to mount the data partition via USB storage, Windows would claim that the device wasn't formatted and offer to format it for you, which, as you can imagine, would be a disaster. The whole ext4 setup is another reason that Android switched to using MTP for transferring files. Most of these devices don't have the necessary kernel configuration to even support USB storage mode, so it's not very easy to enable USB storage if we even wanted to try. Unfortunately at this time, MTP isn't available in recovery, so if you have no other option, you will have to use adb to push and pull files to/from your device.
As a special note, if you choose to do a factory reset from your ROM, even if the ROM says that it will wipe everything including the internal storage, well, that's not what TWRP will do. A stock AOSP recovery would format data including the "sdcard" but TWRP will use its regular factory reset setup that leaves the internal storage intact.
There are a couple of nice gains with using this setup vs the old data + FAT storage partition. With /data/media you, as the user get more control over how you use your storage. If you have a ton of apps, then that's no problem since you have a huge data partition to work with. If you don't have a lot of apps, you get more room to use for storing things like movies. Further, ext4 doesn't suffer from the 4GB file size limit that FAT has, so you can have a large, high-def movie on your device if you like. I'm sure another motivating factor was to get Android away from using FAT which is a Microsoft creation. Performance on ext4 in Android is also probably better than FAT. As a downside, data media devices tend to store a lot more app data in the "data" section and so backups on these devices tend to be larger.
Android 4.2 has changed things with /data/media devices a little bit due to the multi-user support that came in 4.2. Each user is assigned a subfolder in /data/media. The main user gets /data/media/0 and subsequent users get /data/media/10 and /data/media/11 and so on. If you switch users in Android 4.2, the system will remount the /sdcard folder to point to the proper user's folder. TWRP has been updated to use the /data/media/0 folder starting in 2.3.2.0.
Another "feature" of 4.2 is that when you "update" to 4.2 it may attempt to upgrade your /data/media to multi-user. If you're running an older version of TWRP than 2.3.2.0 or newer, a factory reset may trigger multiple upgrades, causing your "sdcard" to get moved to /data/media/0 then /data/media/0/0 and then /data/media/0/0/0 and so on depending on how many times you "upgraded". This may cause backups to not be visible in TWRP. Also, there currently isn't a good way to go back to a 4.1 ROM after using a 4.2 ROM without having to manually move your files around.
Click to expand...
Click to collapse
http://teamw.in/DataMedia
I asked them if it's possible to just mount the ext4 partition if Windows users install some apps that can read them. Will see if they're going to answer.
Hope this helps. Cheers.