The internal FLASH memory is probably dying.
I had this on GalaxyTab 2.
As the number of times one can write to FLASH type of memory,
after some years (?) the device dies.
Repairing is very difficult as you need to replace the FLASH memory chip on the board and program the firmware to the new chip.
You can root the device and change the mount-points of the partitions away from the dead partition or use the external microSD card, but in my case it only worked for some months, then the sdCard gave up.
Then I gave up and bought a new device....