using your external SD card as internal storage with Android 6+
What is "adoptable storage"?
Adoptable Storage was introduced with Android Marshmallow (6.0-marshmallow) to address the permanent issues with too low internal storage (especially on budget devices — see insufficient-memory) by "adopting" external storage to substitute for the internal storage.
If your device supports external SD cards and runs on Android 6.0 or higher, on insertion of a card you will be asked whether to use it as "portable storage" (i.e., the same way you've used it before), or if Android should adopt it as "internal storage":
What happens behind the scenes?
If you chose to "adopt" external storage as internal storage, it will be encrypted. Which means multiple things:
- this storage can only be used in the device it was "encrypted into"1
- you no longer can simply switch it to another device: lacking the encryption key, it will be unreadable there
- you no longer can use a card reader to access the card's content in case your battery run out (or your device gets damaged), to rescue some data
- no "simple upgrade" to another (bigger, healthier, faster) SD card
- all data on the card will be erased while "initializing the adoption". Same applies if you want to revert the process.
- whatever real internal storage you had will become invisible to both mtp and normal (non-root) file management apps, and even then, it can only be accessed with considerable difficulty as a mounted storage.
- when you factory-reset your device, you cannot even use recovery software to rescue data from the card (as the encryption key will be gone as well).
- How Android 6.0 format as internal storage feature works?
- Understanding Adoptive Storage in Android 6 (Marshmallow)
- Adoptable storage in Android 6.0: What it is, how it works
- How to decrypt adopted storage?
- Corrupt SD card formatted as internal storage (answer is a tutorial on how to mount that card on your Linux PC)
- How to split adopted storage? (multiple partitions)
- How can I move data from an adopted SD card to a new SD card?
- How to adopt SD card as internal storage on Samsung devices?