I have a 500gb external hard drive that I'm thinking of using for Time Machine backups. It's about half full now and formatted in NTFS, and as I understand it Time Machine will only work will the Mac OS Journaled format? (even if I installed the NTFS 3G thing which will allow writing to NTFS?) Is there any way I can reformat a partition of the external drive without deleting any content on it to use for Time Machine? Also how much space do Time Machine backups take up? I have a 128gb Macbook Air if that helps.