I have one 2011 mac-mini and one 2010 macbook connected via airport extreme to an external hard disk. The mac-mini (running yosemite) is connected via ethernet and the macbook (running mountain lion) is connected wirelessly. They are both set to automatically make backups using time machine on the same external hard disk. I would like to know whether my backups will be corrupted if the time machine backup starts on both the machines almost at the same time.