"Disk Not Ejected Properly" error after EL Capitan goes to sleep and wakes up again.

Okay, so I can confirm that this doesn't work–at least for me. 😟

Reading how this thread has developed, I should add that the disconnects I experienced happened with a computer that is set to never sleep. Perhaps that is why Keep Drive Spinning works for me -- I also have the "Put hard disks to sleep when possible" box checked, but my sudden disconnects continue to be resolved. Still, reading how different users have found very different solutions, temporary solutions, or no solution -- points to an issue that Apple ought to investigate. Bug reports seem appropriate: https://developer.apple.com/bug-reporting/

Just a quick note - 10.11.4 here now and I can't even complete my first backup with Time Machine due to the disks ejecting, as described here. I don't even know why the mac (brand new MacBook Pro) is going to sleep as I have totally turned off all power nap, disk sleep etc options =(

I have started to just manually eject the LaCie 6T Thunderbolt drive and shut it off before sleeping the iMac. However, when I wake the iMac up, the LaCie 6T thunderbolt drive comes to life, so it's getting some sort of signal from the thunderbolt cable. It does not re-mount, it just spins up. Turning it off and on again does not re-mount the drive on the Mac. THE ONLY THING that works is unplugging and re-plugging the thunderbolt cable. Then it is remounted and everything seems to be fine.

This is all very frustrating. I have tried following the links posted in this thread to submit a bug on the Apple developer site, but I am not a developer. Is there someplace else I can go to bring this issue up with Apple?

Login to Apple Bug Reporter

I believe you only need an Apple ID. Should have given this link before.

[UPDATE]

Okay, it looks my initial tests were wrong. I have now let my MacBook Pro go to sleep on its own on 3 separate occasions and I can confirm that this solution, which I mentioned previously, does now appear to work—at least for me and my USB 3.0 G-Drive. I hope others will find this information helpful as well. Here is the solution:

Here is the solution I found: I connected the drive to a powered USB3 hub that is connected to the USB3 board in the computer. The hub power apparently is enough to allow the computer to sleep and allow the drive to wake when the computer wakes.

FWIW, this is the USB 3.0 Powered Hub that I'm using:

http://www.amazon.com/Satechi-Premium-Aluminum-White-MacBook/dp/B00CIY0KUG?ie=UT F8&psc=1&redirect=true&ref_=oh_aui_detailpage_o00_s00

Kelly, you appear to have found something, here. I plugged the Xiaobi Dual Hard Drive Dock whose disks had been suddenly dismounting into a powered USB 3.0 hub, and -- with the Keep Drive Spinning app's effects disabled (it kept drives mounted for me before this discovery) -- Voila! They stay mounted. Time to modify my bug report.

FWIW, my USB 3.0 powered hub is from Anker -- http://tinyurl.com/zfqybxm

Awesome! That's great to hear.

I'm at sleep number 6 now and no problems so far. (knocking wood)

Kelly, (and myaka too).

I think you did find a good workaround. It "sort of" worked for me, too. Only I had to revert back to 2.0, based on my macmini capabilities.

My macmini was just before the ports were made 3.0. I had purchased the USB 3.0 hub similar to yours. I was still getting this problem. I checked my system info, and found out that the macmini port is 2.0. So I found my old USB 2.0 port (and it also has it's own power source). I plugged it into the main usb 2.0 macmini port and it seems to be behaving, for now.

My macmini is not that old, so I'm not upgrading anytime soon; I'll just have to keep using the usb 2.0. Yeah, 2.0 is slower, but my macmini only can do 2.0, so 3.0 usb hub can't make it faster!

So it goes. Disk mounted on powered USB 3.0 hub at 9:06 this morning. At 2:08 this afternoon, it spontaneously unmounted with no input from me.

Note that my machine continues to be set to never sleep, but the Put hard disks to sleep when possible box in Energy Saver prefs is checked. Maybe unchecking it would offer benefit, but I've got an internal RAID pair that I don't want to spin every blessed second of every day, and that never generates alert messages about ejecting improperly.

I'm back to the Keep Drive Spinning app for my external HD dock so it will only unmount at my command.

myaka, I just checked and in my Energy Saver preferences, "Put hard disks to sleep when possible" is unchecked, so perhaps that's the key to this setup. 🙂

Try clearing your user cache and your root folder library cache. They are in your user and mac HD library folders. That temporarily fixed my problem thus far.

Sadly, deleting user and root cache files (and restarting) had no effect. What is confusing about this issue is that there appear to have been different fixes for different computers and/or configurations -- that some of them appear to have had only temporary effect muddles things yet further.

Did you make sure "Put hard disks to sleep when possible" is unchecked?

When the problem first cropped up, I did try unchecking that box. It made no difference, unfortunately.

BTW, when I made that test, it was an attempt to see if that Energy Saver setting was an issue -- but I would not run the computer for extended lengths of time (weeks, months) with it unchecked unless I only had SSDs affected by that setting.