For months my Macbook said that my startup disk was full and when I checked my storage breakdown I had a mystery 50GB taking up space out of 121GB flash drive. Last week my laptop broke and I had to re-download OS X, wiping the laptop clean. I then added my photos library (47 GB) and music library (8GB) and backed up my iPhone once. After that my laptop once again said I had run out of space. I don't understand how this has happened as since my laptop got wiped there shouldn't be any files cluttering. I downloaded OmniDiskSweeper which said that the biggest users of space are the 47GB taken up by photos (under 'documents') and 41GB of iPhone backups. Is it normal for a single backup to be this big? Can I move the backup onto my external hard drive? Is it reliable to only use iCloud for backing up iPhones? Just not sure what to do, I only have 2GB of space left and I need to resolve this ASAP. Please help!!