"Disk Not Ejected Properly" error after El Capitan

I Found that erasing/formatting my (Brand new) external hard drive and establishing a fresh backup solved my problem.

I had been thinking of trying that but I had been holding off. Didn't want to lose my Time Machine backups. Finally bit the bullet.

Sorry to say, didn't fix the problem. I was able to complete a full Time Machine backup, but as soon as the computer went to sleep, I got the very familiar error message again.

The app Mountain solved my problem! Thanks! I've been running about four weeks without the error message that my disk was ejected improperly. The disk drive stays mounted. I use it for media (iTunes and iPhoto) but not Time Machine backups. Thanks for the tip!

I take it back, my 'solution' mentioned earlier did not work! This must be a Time Machine (which is using the drive) issue, as another USB drive has no problems whatsoever.

Same problem in Belgium: 'Disk not ejected properly' after iMac awakes from sleep. Happens since El Capitan, also after version 10.11.3, also after starting up with the procedure 'alt, cmd, p, r'.

I have exactly the same issue with Lacie 8TB and iMac 2013.

Solved ... Simply remove drivers .. In my case WD My Book. Look for WD+ Turbo Installer and remove drivers. It works for me !!!

Look for WD Macintosh + TURBO Drivers

http://supportdownloads.wdc.com/downloads.aspx?DL

I use a late 2014 iMac Retina 5K 27" with OS X El Capitan version 10.11.3 installed and my WD 3TB USB 3 portable hard drive plugged into a USB port on the back of my Mac. . I've been intermittently receiving the dreaded "disc not ejected properly" error messages after which my WD 3TB My Book disappears from my desktop and Time Machine (which uses the WD for backups) cannot find the WD either. Having read all of the posts in this string and have tried several of the suggested fixes, the only thing that works for me is the following combination:

First, power everything down. Remove the power and USB cables from the portable hard drive (and also remove the power cable from the mains). Reboot the MAC and and wait until the OS is fully loaded. Then plug the power cable into the the hard drive and then the mains and switch on using the power button. Wait a few seconds while hard drive does it's internal checks (the power light may flash to show completion of checks). Now plug the USB cable into the hard drive and then into the Mac (this combination also seems to work if I plug into a USB mains powered hub that I have). After a second or two the my hard drive appears back on my desktop (and reappears in Time Machine which does an immediate backup).

After many years using Windows I switched to a maxed-out Mac expecting/hoping for high performance, reliability and good support. Thus far I am not impressed with having to go through the above 'ritual' just to get access to my data and backups! I believe this to possibly be an El Capitan issue and think it's deplorable that when there are so many forums on the 'net' mentioning this problem, Apple haven't either openly admitted the problem exists and said they're working on a fix, or resolved the issue IF they are capable of doing so.

Good luck, I hope this helps.

Problem solved with update El Capitan 10.11.4

Ran the update. All seemed fine. Disk mounted on restart.

Just got back to wake up the computer and there it is: Disc not ejected properly.

Oh well.

Yes, unfortunately the problem is still there, even with El Capitan 10.11.4.

I have been following this and similar threads for ages now and having bricked an external WD HDD to this problem the only solution I can come to is to back up, eject my drive and unplug until the next time a backup is due. Pretty much doing Time Machine's job!

I do see a change with the latest update.

1. My disk (directly plugged into my iMac USB port) now mounts consistently at startup.

2. After waking from sleep and dismissing the disk not ejected properly message, I hear my disk make some noise (sounds like it is spinning up and down), and then it reappears on my desktop again.

Prior to this update, the only way I could get the disk to mount would be to unplug it and then plug it in again.

I had the same problem on my MacBook Pro 13" Retina 2015 and Transcend JetDrive and apparently i fixed it using this script on github:

https://github.com/syscl/Fix-usb-sleep

it is two days that i am using it and no more error messages about disk not ejected properly.