After downloading 10.10.4 installer from the Mac App Store and creating usb bootable usb drive. I found i with SSD i needed to remove CoreStorage in order to totally wipe the drive from Terminal.. so i used diskutil cs list to find id then deleted this... instead without rebooting (it was quicker) This went well, however u cannot install after partition creation, "Reinstall OS X" and then continue option does not work...... I resolved by by rebooting and all is ok... so my question,, since i used diskutil cs to remove core storage (confirmed both diskutil list, and also DiskUtility showed "Unformatted" why was a reboot required to fix ? I thought diskutil cs command was there to remove. I was booted of usb at the time Also, why is Core Storage removal only required on SSD, not spinning hard drives.... ? My 500Gig Mac mini went through no problem, and is running Yosemite.