So the last time I backed up my mac book pro 13" 2010 was right before Mavericks was released. I was previously running snow leopard. I was reluctant to hook up my external hard drive because I was hearing stories of people's external HDD's being erased once they connected it to their computers after upgrading to Mavericks. Last night I wanted to back up all my files to the external hdd. When I pressed the time machine icon on top I got a PREPARING BACKUP message. This message was there for quite a while. It eventually started backing up but at a very slow pace. I then just stopped the back up because it was taking a long long time. What is causing this?