I want to kill my old Macintosh HD Partition which is on the HDD. I am running of the SSD now. It works fine when I disconnect the HDD entirely, thus it shouldn't be a problem to delete the old one (all data is save). It doesn't seem to work though. It always says (even in Windows) that it is in use and cannot be unmounted. I want my HDD to become a data only disk and offer no bootable volumes but I just cannot seem to delete any. I didn't try the 2 NTFS volumes because I still need some data from them. But in Windows they shouldn't be a problem. My partitions look like this MacSSD boots WinSSD (x64 new) boots Macintosh HD boots if selected and doesn't let me unmount it Windows x86 none bootable, unmounts Bootcamp (x64 old) boots both HDD Win partitions, unmounts Now the HDD even spun down but as soon as I enter diskutility, it spins up and unmounting is not allowed. Any suggestions. The only step left I can think of is. Dave all the Windows data. Take out the HDD put it into my Windows Desktop and delete all the partitions there. Seems extreme and I would have to disassemble it again. I tried to delete the whole partition in Windows (boot WinSSD) but next MacSSD startup it was back as though nothing ever happened.