Samsung devices don't support Adoptable Storage. However, there is a workaround with ADB (root not required). Here are the commands for ADB:
adb shell
sm list-disks
partition DISK private
reboot
Notes:
- DISK needs to be replaced with the output of the previous command. For example
partition disk:179,64 private.- If you don't want to convert the whole disk, then use this command instead:
partition DISK mixed VALUE, where VALUE is the percentage (0-100) to keep as external storage.- Reboot is optional, but recommend, so all apps detect the external storage.
If you have root access, you can use my app [Root Essentials][1] instead. It can do all of this automatically without a PC or terminal commands.