Since Android 6.0 (Marshmellow), Android supports Adoptable Storage. However, many phone manufacturers, including Samsung, have disabled this feature on their phones.
How to use Adoptable Storage on supported devices:
If you do have a phone that supports this feature, you can turn it on by following these instructions:
- Put an SD card in your device.
- Open "Settings", "Storage", the SD card, click the three vertical dots, and press "Storage Settings".
- Tap "Format as Internal".
What it does:
Here's how Adoptable Storage works, according to source.android.com:
When external storage media is adopted, it’s formatted and encrypted to only work with a single Android device at a time. Because the media is strongly tied to the Android device that adopted it, it can safely store both apps and private data for all users.
Apps can be placed on adopted storage media only when the developer has indicated support through the
android:installLocation attribute. New installs of supported apps are automatically placed on the storage device with the most free space, and users can move supported apps between storage devices in the Settings app. Apps moved to adopted media are remembered while the media is ejected, and return when the media is reinserted.
So not only does the device have to support Adoptable Storage, but the apps have indicate support for it too to be able to be stored on the SD card.