Disk not ejected properly

JScott has mentioned that he's seeing the DNEP error with Firewire-connected drives. The thread has gotten too long to easily read all 33 pages, but I thought I'd ask if anyone following has seen it with Thunderbolt-connected drives.

Since upgrading to macOS Sierra, my USB connected drives have mostly been error free, but I now see the DNEP message for my TB drives every time after my iMac 5K has been sleeping overnight (sleeping it for an hour or two during the work day does not seem to do it). Only once have I experienced an actual problem other than the annoyance of deleting the error messages. On one occasion, Sierra somehow created an alias for my external drive, and I suspect that it was related to this DNEP issue. That changed the name of the drive's Mount Point ("Data 1" was changed to "Data 1 1", and that name change caused confusion for several applications that were set to create backups to that drive.

Anyone seeing the DNEP with Thunderbolt-connected drives?

Actually, my FireWire drive is connected to my 2015 iMac via Thunderbolt (failed to include that detail, I see). I use an Apple Thunderbolt to FireWire connector. So, yes, technically my drive is Thunderbolt connected.

Since I posted my update on January 7th, I have seen a few more DNEP errors, though not as many as I had been seeing in December. They do occur after overnight or longer sleep, not after brief sleep, like Milleron's report. I have not experienced seeing an alias getting created. I am still on Yosemite but will upgrade to Sierra one of these weekends.

There's been much talk of this issue going away with an upgrade to Sierra. For me, that is not the case. My mid-2009 Macbook Pro running Yosemite was handling my 3 external LaCie drives just fine. 2 are daisy-chained Firewire, and 1 is USB. None of these drives have their own power-supplies, but are powered by the data ports (travel-drives). They've always treated me great.
Last month I bought a new MacBook Pro and migrated my system from my old machine. The new machine came with El Cap and the involuntary dismounts (also a mtn. biking term) started right away. I can get a dozen error messages on my desktop. I read this thread and was inspired by the theory that Sierra was the fix, so I jumped on that upgrade. Nothing has changed. Interestingly, it seems to only be the Firewire drives (now running through a Thunderbolt adapter) that are having the issue. The USB drive seems to be solid. I have tried both suggested fixes: Energy Saver "Put HDs to sleep...." setting; and the Spotlight, adding drives to Privacy list...with a system restart for good measure...to no avail. I have Time Machine disabled (using it manually, periodically). Since my machine is new, I'm going to call Apple support and try to get a fix, or at least some acknowledgment, right from the horse's mouth..

"Plus one" on the Sierra doesn't fix the problem. Neither does moving to a new Macbook Pro.

I have a brand new, MacBook Pro (15-inch, 2016) with touch bar, etc. that came stock with macOS Sierra (upgraded now to ver. 10.12.4.) I get 14 DNEP errors on my desktop every time I come back to my desk and wake my machine. I have one 2TB Seagate GoFlex Desk Media drive that I use for Time Machine backups.

C'mon Apple. This is an ISSUE. Please address it.

BTW, this also happened on my last MacBook Pro, which was a 2013 model. This is an OS issue. It is not drive or cable or even Apple machine version dependent. Please put some unimaginably smart engineer (I know you have many of them) on this and find the bug. It's certainly not hard to reproduce, and you have about a thousand of us that have the problem who would love to test it for you.

Please? Please, oh please.

I ran into the same problem. In my case, the culprit was the type of surge suppressor I was using. This is the kind that turns off power to all the the outlets when the main outlet senses that the device plugged into it has powered off. When my iMac, plugged into the main outlet, went to sleep, this was sufficient to turn off power to all the other outlets, including those that my external drives were plugged into. After I plugged those drives into a second surge suppressor, they now remain powered on when the iMac is sleeping and I no longer get the "Disk not ejected properly" message. An added bonus is that the drives spin down during sleep, whether or not I tick the "Put hard disks to sleep when possible" checkbox in Energy Saver, and whether or not I select the "Automatic" setting on the drives' three-position on/off switch.

If I connect my USB hard drive with my PCIe USB 3 card, the problem always happens, despite I have tried all the suggestions.

However, if I connect it with my USB 2 (on the back or front of my Mac Pro 5.1), the issue gone and no more message pop up.

I'm going crazy, imac retina 5k and new usb 3 seagate 2tb i got ever "Disk Not Ejected Properly" telephone support will not admit the bug, told me that the disc is defective. I have no words...

Same issue with a 27" iMAC, 1 week old.

Same issue, iMac Late 2013

Same issue with my MacBook Pro 15-inch, Early 2011

I too had the same issue. Apple support didn't have a solution. Bought the app "Jettison" and it totally solved the problem.

Just had a chat with Apple Support. They suggested enabling Power Nap. I'll give it a try this weekend (with a non-critical drive) and post whether or not it helps.

I don't believe the Power Nap option will work. I have the same problem and have had that enabled for a while. If you get better results, let us know.

Sounds like you took the same path that I took. I too purchased Jettison which seems to be working. And yes, you would think that Apple could provide an even better fix - long overdue IMO

I have a 27" iMac 2010. The hard drive was replaced last year. Using a Western Digital back-up drive. I have the same problem.