[GUIDE] EXT4 microSD card on Dell Venue 8 7840 topic

The tablet supports up to 512gb microSD cards but only the FAT32 filesystem by default - not much use if you're dumping large files (>4gb) onto them.

Notes:
I've only tried this with a pre-formatted ext4 card. The stock Dell rom does not ship with mkfs.ext4 binary so I highly doubt you'll be able to format the sdcard as ext4 on the device itself. I also have no idea what happens if you subsequently try to use a FAT32 formatted microSD card. I also haven't tested hotplugging - again, I assume it would work but it's untested.

I stress, be very careful when performing these steps. The bootloaders on these devices currently cannot be unlocked and we only have a tethered CWM at the moment.

I'm not responsible if you brick your device trying to follow the steps.

Requirements:

• Root access


• Busybox


• Terminal emulator/adb shell/ssh access


• Pre-formatted ext4 sdcard

Steps:

• Download hxxps://dl.dropboxusercontent.com/u/134520/.nemaz_ma/vold.ext4support.tar.gz on the tablet (replace hxxp with http, I can't post links)(found here: hxxp://forum.xda-developers.com/showthread.php?t=2580142)


• Open terminal emulator
  
  
  

  Code:

  
  

  ---

  cd /sdcard/Download
tar -xvf ./vold.ext4support.tar.gz
su
mount -o remount,rw /system /system
mv /system/bin/vold /system/bin/vold.bak
cp ./vold /system/bin/vold
chmod 0755 /system/bin/vold

  ---

  
  


• Reboot the device

If you're lucky and open Settings->Storage, you should now see the sdcard showing up.
If not:

• Open terminal emulator
  
  
  

  Code:

  
  

  ---

  cd /etc
vi vold.fstab

  ---

  
  


• Most lines in the vold.fstab file are comments, there should be two lines at the bottom:
  
  
  

  Code:

  
  

  ---

  dev_mount sdcard_ext /storage/sdcard_ext auto /devices/pci0000:00/0000:00:01.2/mmc_host/mmc1 /devices/pci0000:00/0000:00:11.0/dwc3-device.1/gadget/lun0
dev_mount usbcard /storage/usbcard auto */block/sd

  ---

  
  
  you need to change
  
  
  

  Code:

  
  

  ---

  dev_mount sdcard_ext /storage/sdcard_ext auto /devices/pci0000:00/0000:00:01.2/mmc_host/mmc1 /devices/pci0000:00/0000:00:11.0/dwc3-device.1/gadget/lun0

  ---

  
  
  to
  
  
  

  Code:

  
  

  ---

  dev_mount sdcard_ext /storage/sdcard1 auto /devices/pci0000:00/0000:00:01.2/mmc_host/mmc1 /devices/pci0000:00/0000:00:11.0/dwc3-device.1/gadget/lun0

  ---

  
  
  (you're changing the third parameter from /storage/sdcard_ext to /storage/sdcard1)
  


• Give the device a reboot and it should now work.

To undo the patch:

• Open terminal emulator
  
  
  

  Code:

  
  

  ---

  su
mount -o remount,rw /system /system/
mv /system/bin/vold /system/bin/vold_ext4
mv /system/bin/vold.bak /system/bin/vold

  ---

  
  


• Reboot

Good luck.