Need to free up my 2010 mac mini HD space. I have over 200 GB of music on it. It is backed up by firewire to a 300 GB EHD. Thinking about adding another EHD by USB and use it as a clone. Will itunes run slower if it is on an USB EHD of should I run itunes from the firewire. Any suggestions on brands of EHD? Iomega seems to be good value and I could get it with firewire.