I am relatively inexperienced as this would be my first time switching a hard drive to SSD. I connected the 250gb Samsung 850 EVO SSD to my mid 2011 iMac via a Sata to USB cable but my iMac will not mount the drive for me to clone my existing hard drive. My iMac is running El Capitan OS-X. I apologize if I left any information out. Any help would be great if am stumped.