Gingerbread,Honeycomb, Jelly Bean,KIt Kat,Lollipop,Cyanogen Mod... if i can remember correctly ..
all use the same format.....
i had an SD that had files/file system from GB,HC,and JB...it was a wreck and looked like my brain....but,it still stored junk with the other junk...
sooooo......if you've read this far...... every OS installs a file system on SD ....
sorry if that was all stupid and useless...there just thoughts...i'm no pro....
and i didnt format my SD before or after flashing CM12.1 .....no reason too...i use every other thing on it on every flash for back up and what not..
so ...maybe that point makes my whole comment irrelevant ....
which is no surprise to me or anyone else that's read my reckless meanderings and wondered how i did it and am so dumb at the same time