Up until Yosemite, I never had this as seen in the attached pic. It is an extra greyed out Macintosh Drive listed (before the Recovery Partition) entry which shows the full disk size, same as the regular macintosh listing, but nothing more. There doesn't seem to be any extra partition there. Does anyone know what is going on there? Any way to get rid of it without reformat? I can run a repair disk on it but it shows up no where else on my imac.Thanks.