I had strange error recently. I was using my 1 TB external hard drive as my Time Machine backup from past 2 years(from Mac OS X Lion to MAC OS X Mavericks). Everything was working fine till last night. When I plugged in my External disk it was not recognized at all. So I did go to DISK UTILITY and checked it was showing on it but greyed out. So i tried to repair the disk, but got error saying disk is corrupted and not readable. Not sure how this happened and i thought disk is corrupted. So I connected external disk to my linux machine and try to read, guess what everything was perfectly fine and i was able to read the disk without any issue at all. So i copied all my data back to linux drive and formatted this disk on linux to FAT32. Then connected it back to Mavericks and it was recognized without any issue at all. So formatted it back to Mac OS Extended (Journaled) and did a time machine backup and everything is back to normal. Is this a known issue or did anybody experienced it? Just curious.