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

My G-Drive is listed as external.

Yes, indeed. This is becoming stranger with every post. I'm tempted to do a SMC reset, but my drive is working so well I don't want to screw it up. I need an app to test data transfer speeds so I can see how fast the bus really is.

That is strange. The G-drive is clearly a 3.0 drive. And it is showing USB 2.0 Bus.

Mine all show up as USB 2.0 Bus (which is what they should be). I have a 3.0 flash drive connected and it reports that correctly. I am currently running El Cap 10.11.3.

I've always had such trust that System Information was reporting everything correctly.

OK, now after resetting the NVRAM I have tried sleeping and re-waking my iMac two times. The first time resulted in the (previously unaffected) USB 3.0 G-Drives to both be ejected spontaneously and then remounted by themselves. I did a backup and then slept everything again. This time, all three external drives have come back... That's TWO sleep/wake cycles and TWO successful remounts of the thunderbolt drive. (The one that hasn't remounted after sleep in the past month.)

So resetting the NVRAM has done something. Fingers crossed.

Hi Jim,

My setup is similar to yours and I am experiencing exactly the same problems... but only after updating to El Capitan.

My setup is like this:

Late 2014 iMac 27" 5K, i7

Easy Acc USB 3.0 Hub

LaCie Thunderbolt 2 2big 12TB, running in RAID 0 (Hardware-Raid) connected to Thunderbolt Port

BenQ V2400W Monitor connected to the other Thunderbolt Port via Apples DVI adapter

WD 6TB MyBook USB3.0 connected directly to a USB Port on the Mac

The LaCie is ejecting itself from time to time with no reason, always after longer sleep periods. Mountain.app helped a little (error messages are not after every sleep), but the drive disappears after longer sleep periods. only plugging it out and in again makes it work again.

So far no Problems with the USB connected WD, but this is only connected while I am doing my CCC backups.

Other USB issues are a Superdrive that does not work if it is plugged in while the system is running. It will only accept discs after a restart. Discs cannot be ejected by pressing the eject Key on my Keyboard at all.

My system came with Yosemite, I have been running it for 9 Month without any Problem. This points directly to El Capitan. Called the Apple Help, all suggestions are also posted here but no change in the end.

So like you I am pretty messed up with El Cap. I am hoping that Apple will do something soon.

Jim and Kelly -- System Report on my machine shows my drives connected to a USB 3.0 bus, which is not native to my Mac Pro. I do have the sense that the reporting there may not be connected to the issue -- there have been misreported items in its prior iterations. Here's mine, fwiw:

Only the drives connected via the USB-SATA bridge in my Xiaboi dock disconnect. Two other external drives (Sans Digitals), connected to the same PCI-E USB 3.0 card, one directly and one through a powered USB 3.0 hub, do not ever spontaneously unmount. I may have to blame my issue on the Xiaobi, but the strange, similar experiences others have appear to point to a possible OS X issue.

Kelly -- btw -- I have reset NVRAM multiple times without effect. I haven't reset the SMC yet...

I am at 4 sleep/wake cycles now without an ejection of any external drives. This is after resetting the NVRAM. I never reset the SMC. Things are definitely different after the NVRAM reset.

IN the midst of all my attempts to fix this problem and find a workaround, I installed Mountian app and it didnt work at all. Oddly, it also showed one of my external Gdrives as "internal". When I unmounted my thunderbolt drive with Mountain it was unable to locate or remount it after waking from sleep. When I first reset my NVRAM and had my USB 3.0 Gdrives unmount and remount themselves, I believe it was Mountain causing the trouble because it had just restarted itself when I logged in after restarting. I quit Mountain and trashed it and have not had an ejection since. Also, their tech support apparently does not exist. Total waste of $6 for me.

That's good news. How does one reset the NVRAM on a MacBook Pro?

How to Reset NVRAM on your Mac - Apple Support

Basically a double PRAM reset. Thanks!

Had to edit my formerly positive post. Well, Kelly -- your suggestion of an SMC and NVRAM reset yielded some results -- for about four hours. But the affected disk just unmounted, followed instantly by the Disk Not Ejected Proplerly alert. Why/how it managed four hours of uninterrupted presence on my desktop is puzzling -- particularly since it would have only lasted minutes before the resets. Go figure.

Well that's good news–I hope. Fingers crossed here too. I may try doing the same on my end to see if it clears up my Apple Profiler USB reporting issues.

This was a constant problem for me through the last two versions of software. I leave my machine on almost all the time and often have safari open. Two weeks ago I switched to Chrome as my browser and the problem has not occurred since. I had disabled spotlight search from al my external drives and that had none nothing. I hope this helps some of you. If it should recur I will post that.

To all of you who have invested so much time and effort on this THANKS.

My conclusion after dealing with this for over two years is that there is no answer. I have tried almost everything.

I now just leave my machine on all the time with the energy saver set for never and quit all programs that are complex enough to make the computer fan go to high.

It also impresses me that after at least a hundred of these messages I have never had a disk problem. In fact, almost all the time the disks - I have 5 running off a USB 3 powered hub - show as active on my desktop and only the notice tells me they may have been actually ejected.

Obviously, Apple is not in the mood to address this.

It's Back to using Keep Drive Spinning for me. Too bad it seems not to work for others -- which is another of many puzzling pieces to this issue. I've clocked sixteen hours or so since my last post without an unmount, and past experience tells me I'll not have any, ever, this way. Instead of adding to my bug report, I'm off to thank the author of Keep Drive Spinning.

I had two full days of sleeping and waking the iMac and no ejections until just now.

"Dammm, El Capitan, back at it again with the thunderbolt drive spontaneous ejections."

LaCie 6T Thunderbolt2 drive mounted upon waking, and then ejected itself about 2 minutes later with a "Disk Not Ejected Properly" error.

Is anyone from Apple reading these posts? Anyone from Apple responding to Bug Reports?