One of the new features in Android 6.0 Marshmallow is the ability to treat microSD cards as if they were internal storage. If you have a cheap phone with 8GB of storage or less, this can let you easily double or quadruple your available storage space for just a few bucks.
But if you’ve got a more expensive phone with a decent amount of built-in storage space, you might want to think twice before formatting a microSD card for use as internal storage, because there are some potentially unpleasant side effects.
Android app developer StereoMatch did a little experimenting and discovered a few things about the way Android 6.0 lets you adopt external storage devices as internal storage that aren’t really all that clear from Google’s description.
In a nutshell, when Android 6.0 sees that you’ve inserted a microSD card the operating system will ask if you’d like to treat it as portable storage or as internal storage.
If you choose portable storage, it’ll be treated the same way as removable storage devices have been for the past few versions of Android: you can’t easily install apps to the storage card, but some app data can be saved there and you can store music, movies, photos, and other content on the microSD card.
Choose internal storage and the microSD card will be reformatted and encrypted. Once this is done, the card can only be used as internal storage. If you try to eject the card and read it on a computer, it won’t work. All data on the card will also be erased, so you may want to back up anything important first. Android does provide an option to migrate it, but early reports suggest it’s unreliable.
After you’ve formatted your microSD card, your phone will treat it as your primary storage space. In fact, if you navigate to the Storage & USB section of your Android Settings,
you won’t even see how much internal storage space is available anymore. You’ll only see free space on your microSD card. And if you use a file browser to navigate internal storage, it’ll only show your microSD card — there’s no simple way to copy files to and from the real internal storage. you’ll be able to see how much storage is used and how much is free — but you can only explore the SD card storage, not the internal storage. And if you use a third-party file explorer or connect your device to a computer, you won’t be able to navigate to internal storage at all.
You can still choose to have apps installed to either the true internal storage or your microSD card that’s been formatted to behave like internal storage. But if you had a phone with 8GB of storage and a 32GB microSD card, you’ll only have 32GB of space for music, movies, games, or other files, not 40GB.
Here’s why this matters: the built-in storage is almost certainly faster than any microSD card you’re using. You’ll see the biggest hit if you try to install apps to the removable storage card. But even with files and data loaded on the microSD card, your device might perform some tasks more slowly.
So if you’ve got a phone with 32GB of fast storage, you’ll probably want to avoid formatting your microSD card as if it were internal storage. It’d restrict your ability to access your speedier eMMC storage.
On the other hand, if you’ve got a cheap Android One handset or another device with just 4GB or 8GB of built-in storage, you might be willing to trade off a slight decrease in speed for a big boost in the amount of available storage space.