booting Android from SD card The device model is Samsung Galaxy Note 8.0 (gt n5100)
It's not booted yet had developer mode activated.

The flash memory is completely broken (which probably means the bootloader is gone as well?), and since a simple repair at a shop would cost more than 150 USD, I've decided to give it a last try by copying an Android system onto the SD card to make the device at least function again.

I think I will kind of figure out the last step by myself since I'm on Linux all the time, but I'm not quite sure how to change the boot order or whether it is possible at all.

Is it possible to create a "bootable SD card" to boot Android from on this device – and if so, how is this done?
I have been successfully able to boot from SD card on QMobile Z8 by:


Replicating eMMC partition table by partitioning SD card on a Ubuntu machine using parted and fdisk
Flashing factory firmware images to these newly created partitions using dd
Modifying fstab.qcom &amp; init.tegra.rc files in kernel (boot.img) and recovery.fstab and uneventd.rc files in TWRP recovery to initiate mounting and booting from SDCard instead of internal memory


It was successful after some experiments. I think this method should be applicable to any device with similar configuration. However, files to be edited may vary from device to device.  

If you want to put only apps' external data to SD card and not the whole partition, you can edit fstab in boot.img and storage list in framework-res.apk on Android 5 and older.

For more details: [HOW TO] BOOT FROM SD CARD [SUCCESSFULLY] on QMobile Z8 with BRICKED/DEAD eMMC