Google has been known to dislike the use of external storage on Android devices, which explains why none of the Nexus smartphones and tablets had a microSD card slot. Google’s position is understandable from a software engineering point of view but clashed with popular consumer demand. In Android M, however, Google makes an almost complete U-turn and has found a compromise to the problem, finally providing an official way for users to move apps to removable storage. It has a strange name for it too, calling it “Adoptable Storage Devices”.
There is a reason for the name, however. You are, after all, adopting an external storage to become part of the internal storage. Technically, what it does is it formats the external storage similar to internal one and wraps it in a layer of encryption. Bottom line is that to Android, it’s just part of a now larger storage layout. For users, it means they can move an app’s code as well as its private data to that external storage freely, without having to resort to third party tools or OEM hacks.
Even better, users can actually migrate their “primary shared storage”, the /sdcard directory which is the main storage that users see, to any adopted storage device. While it does allay Google’s worries about security, it still runs the risk of the external storage being pulled out at any given time.
Yes, pulled out. At the moment, Adoptable Storage Devices not only supports microSD cards, which you might expect, but even USB OTG drives, which is somewhat surprising. You will hardly keep a smartphone or tablet always connected to an external hard drive or USB stick, but this is probably both for testing purposes and for Android TV devices which might have a permanently connected external storage.
This feature is available right now in the Android M Preview, though an ADB (android debug bridge) command is needed to activate it. And while this might sound like a relief, users should still exercise the same caution when moving apps and data from internal storage to one that can be more easily removed.
SOURCE: +Jeff Sharkey