I replaced my previous 32GB microsd in my note 3, with a transcend 64GB, and the system asked me if I wanted to use it as extended internal storage. Why not, I never use the sd as swappable storage anyway, and I liked the encrypted storage.
Go ahead an hour, I notice the system filled up 30GB more than the starting space, just stealing it from the sd card for no reason. Also, after rebooting I get a message saying “system has stopped responding”, and swiftkey cannot load languages anymore, disabling altogether the swype function.
I fiddle for good 15 minutes into the settings, finding nothing apparent, until I went into:
Settings > USB and Storage > Internal storage > Options > Migrate
which was supposed to migrate the data from the sd back into the builtin storage.
I started the process and went to sleep (it was late) hoping to find it solved in the morning… too bad! Couldn’t do that, the morning after the internal storage was 100% filled, an error message appeared, and the 60GB sd was still hald full.
The system went from the original 16GB used in the internal storage, to a total of 30GB filled internal storage+roughly 30GB inside the external, which is 60GB used storage… for what? God knows! In the USB&Storage panel of the settings, the details of the used space still amounted to the real space needed, and nothing was there to account for the additional space taken that was reported in the summarized stats…
Hence, I tried copying all the contents from the sd/internal storage to the PC, with the intention of resetting everything afterwards and restoring the data, but using the USB communication resulted in a severely slow transfer speed (we’re talking about a 100Kb file each few seconds, and there were 12GB of data to move).
I tried several times to check and see if I could speed things up, to no avail, so I used the remaining free space on the microsd (I had that, if you don’t you may want to use an OTG cable and a pendrive) to create a ZIP archive (with estrongs) of all the contents of the internal storage, and as a single file like that I could then copy it to my PC at a decent speed.
Once that was done, I wend in settings > USB and storage > SD card > options > format as portable, agreeing to lose all data (I had backed it up anyway), then into recovery I wiped the internal storage, then rebooted to have the changes take effect, and from this state (internal storage almost empty, microsd seen as normal portable storage) I copied over the backed up contents from the previous configuration via normal USB transfer (some files and folders couldn’t be copied, but it was nothing essential).
Up until now eveything looks to have gone back to normal.