I have 2 external drives connected to my Macbook Air with internal SSD - a Time Machine drive, and external storage drive for large files I don't need on my SSD (eg movies.) On an almost constant basis, OS X is hanging with the beach ball while the drives spin up. I realise hard disks 'sleep' and are not always ready to seek, but my two major annoyances are that it does it very often doing things that don't require the disk (eg clicking on a link in a browser) and for the few seconds it is spinning up, the entire system hangs with the beach ball. A few seconds might not sound like much, but when it is doing it every 10 minutes all day long it gets very tiresome and frustrating. I would expect it to happen if I'm saving something or the hourly time machine backup is about to start, but why does clicking a browser link require access to an external drive? And why does spinning up a drive need to cause the system to hang? I can't remember exactly when it started happening, I know it was also doing it in Yosemite so it's not exclusive to El Capitan. I know there is an option in Preferences to stop putting hard disks to sleep, but surely that will shorten the life o the drive and as above I don't see why it is necessary - I am not using apps that require the drive, and if what I'm doing doesn't need the drive, why the beach ball? This problem has really started to bug me recently, I have been using a multi-drive setup for years and don't recall it happening in earlier versions of OS X.