I have a Toshiba Class 10 64GB microSD that I want to use in a tablet (Cyanogenmod 11) by formatting it ext4.
So I did the usual thing (under Fedora 20): created a single Linux partition with sfdisk, then created the ext4 partition with
mkfs.ext4 /dev/sdf1 without problems. Then, I just tried to mount it with
mount -t ext4 /dev/sdf1 /mnt/sd/, but I got a journal error:
JBD2: no valid journal superblock found EXT4-fs (sdf1): error loading journal
Tried googling this, but didn't find anything useful.