I have a Late 2013 27" iMac with 256Gb internal SSD. I also have a WD 4TB My Book desktop external HD that I use for mostly all my iTunes media, photos, etc. Every time it spins up and down, it slows down my mac considerably for about 3-5 seconds - almost to the point of freezing the machine. I don't understand why it will randomly spin up when I'm not accessing files on the drive. For example, if I simply launch Chrome browser to visit a webpage, it will spin up and I have to wait 5 seconds for it to finish. It's so annoying. Is there a way to limit when it spins up/down? In the Energy Saver settings, should I have the "Put the hard drives to sleep when possible" checked or unchecked? I want to buy a 3TB or 4TB SSD, but they are so expensive still. I have been thinking about getting a 1TB SSD for now just for my iTunes media, which is about 700Gb alone. Or just start streaming my iTunes media from the cloud. I don't really see a huge need for downloading everything nowadays. My internet connection is very stable and fast. Then just keep everything else on the internal SSD, which isn't much. My iTunes media library doesn't grow that fast anymore, so I think 1TB SSD might hold me over for awhile until the prices comes down on the larger ones. Thanks for any advice or help!