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:**

> 1. `<DISK>` needs to be replaced with the output of the previous command. For example  `partition disk:179,64 private`.
> 2. 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.  For example `partition disk:179,64 mixed 50` for 50%.
> 3. Reboot is optional, but recommend, so all apps detect the external storage.

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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.


  [1]: https://play.google.com/store/apps/details?id=com.superthomaslab.rootessentials