Update Desperately Needed for Yosemite

I also have a My Book for Mac that I received last year for Christmas so it is fairly new that has stopped backing up since I upgraded to Yosemite on my iMac. I tried running disk repair and it says it is a read only disk. I need this to work ASAP. This is my only backup at the moment and it’s not working. Any idea when this compatibility issue will be fixed?