Hello, I recently purchased a new iMac 27" and went with the 256 GB SSD internal storage based on some research I did. My question is, what is my best option for an external drive for additional storage? I would like to use it for backup and for normal storage of less frequently used files. I'm not a tech expert by any means so I'm looking for an easy option that won't cost and arm and a leg. Thanks in advance for any thelp.