I just created account to answer this post. I managed succesfully perform this operation on my LG K8 LTE. I want to answer on all of "500 xxx Unknown disk" errors problems. Solution is very simple.
Problem is that author created his post somehow erroneously, so that we first show list of our disks, and thenwe show list of our VOLUMES. But for shell DISK is not the same as VOLUME. So we simply make error when typing:
" sm list-volumes all"
Because after that, we type VOLUME id in command:
sm partition disk:HERE private
Instead of a DISK id. So we need simply get DISK id. Proper steps would be (lines with // means this is my comment and do not type this ;) ):
// HERE YOU GET YOUR DISK ID, SOMETHING LIKE "disk:179,64" - REMEMBER THOSE NUMBERS
sm set-force-adoptable true
// IN NEXT LINE, SIMPLY PUT THOSE NUMBERS AFTER "disk:" AND ALSO AFTER WORD "mixed" TYPE PERCENTAGE OF SPACE LEFT AS EXTERNAL, SO IN MY CASE:
sm partition disk:179,64 mixed 60
// IT TAKES TIME. BE PATIENT. WITH THIS LINE I TRANSFORMED WHOLE EXTERNAL SD INTO 40% OF INTERNAL AND 60% OF EXTERNAL
sm set-force-adoptable false
BANG! That's it! Now go to storage and usb, there click on internal part of SD and expand options, click on "use as internal" or something like that, last option, I cannot see what was that because I already clicked it and everything works, apps are finally going on SD with OBB files! ;)
Have a good day!