Anyone else having this problem? I have 2 usb3 external drives, both just over a year old, both not working after the latest Mavericks update. One drive is just Time Machine, the other bigger drive is partitioned with TM and Cabon Copy Cloner. When the latter refused to backup, thought the disk was faulty, erased, partitioned again, still wouldn't work. Tried the TM-only disk, it starts but then gets stuck. Both worked perfectly when I backed up before the update. Called Apple. I'm reluctant to do a clean install when I can't first do TM backup. So Apple Support suggested a fresh OS install via recovery partition. Did that, then repaired permissions. Made no difference. Would be helpful to know if this is happening to anyone else before I take the next step. Thanks.