As noted on a different thread, I seem to have developed an issue with the Time Machine partition on my external backup drive -- there is one other partition on the drive. After a few backup errors, I tried running Disk Verify, which got an error code and then Disk Repair, which got the following error code: "File System Check Exit Code 8." Last night I plugged the external drive into a different Mac. The second partition seems fine. But for the Time Machine partition, I got another error and this message: "OS X Can't Repair Disk: You can still open or copy files on the disk, but you cant save changes to files on the disk. Back up the disk and reformat it as soon as you can." Before I reformat the Time Machine partition, I want to make sure that I'm not at risk (or a significant risk) of losing the data on the second partition. I expect the answer I'll get is: Back up the second partition first. However, since this is my back up disk, that would require me to buy or borrow a new drive with at least 300gb free storage. Not so easy. So -- should I go ahead and reformat the Time Machine partition? Or should I take the effort to back up my second partition before doing so? Or is there another fix?