I have a Firewire drive connected to my iMac and sharing enabled. 2 MacBook Airs then connect wirelessly to the same network and backup to the drive. It has worked perfectly for the last couple of years with Lion and Mountain Lion. Yesterday I upgraded to Mavericks and now neither laptop can see the shared drive in Time Machine, although the drive displays quite happily in Finder. I have disabled and re-enabled sharing. Booted and re-plugged the drive in and still when I go to Time Machine preferences and select drive, nothing is listed. Any ideas?