What filesystem has the micro SD? It's usually FAT32 by default, but if your microSD has NTFS sometimes it gives problems in Android, both filesystems are property of Microsoft and the companies have to pay royalties to use it. FAT32 is 32 bits and the file size no more than 3,5 GB each one.
If you will only use the microSD with Android I'll recomend you Ext4 or ReiserFS, more info
here about both filesystems. You need any Linux distribution to do it, Windows won't recognize the microSD.