So I'm on Marshmallow and have formatted my SD card as internal storage. Its filesystem got corrupt two weeks later for some reason.
Plugging it to GParted, I see 16MB of FAT32 and the rest is an unrecognized filesystem. It's not unformatted, just unrecognized.
GParted is giving the "Unable to read the contents of the fileystem." error for both partitions, though the FAT32 partition is accessible from File Browser flawlessly.
It's a Samsung i9505 running on nightly built Cyanogenmod 13.
EDIT: I found out the unrecognized partitions is a static AES-128 bit encrypted ext4. Now I will try to decrypt it and recover whatever.
EDIT2: I changed my mind and won't bother. Formatting as external storage this time.