Recently had updates installed on iMac for Lion os. Now my 2TB WD external HD will not back-up. Disc Utility says it cannot repair the disc and that I must back-up as many of my files as possible and then reformat the disc and restore backed up files, but I have over one and a half TB's of files on the external drive and very little available space on the imac's internal drive. What is the point of installing updates to make an os work more efficiently when in fact it just causes more problems? Do I now have to purchase another large external HD just to transfer my existing files onto before reformatting the WD drive and then transfer the files back onto the WD or is there any other option?