I am suddenly in a bit of a panic situation. My backup drive, the disk meant to keep my data safe, is failing. Files I still have on my main disk, as well as a few files that only exist on the external disk due to a need to manage things like a bloated iTunes library, are now corrupted or just zeroed out. I am in a rush to get everything that's still intact, onto the main disk, and then on to DVDs if possible. I'll literally have no real backup until I can replace the disk. This happening so close to the official launch date of El Capitan worries me, because I was hoping to have important files duplicated on the backup disk before I upgraded. How screwed am I?