Which disk was not ejected properly?

Try disconnecting all your hard drives, then reconnect them one at a time. This should allow you to determine which drive is causing the problem.

Modern Pixel wrote:

But the problem is that all of my disks are mounted fine.

In that case, just before you put your machine to sleep, why not try dismounting all disks except your Macintosh HD drive? Then you could remount them upon awakening. Maybe that will clear out this issue.

I'm suggesting this as a one-time exercise - I'm not suggesting you do this routinely and repeatedly.

The next time you have the problem, note the exact time: hour, minute, second.

If you have more than one user account, these instructions must be carried out as an administrator.

Launch the Console application in any of the following ways:

☞ Enter the first few letters of its name into a Spotlight search. Select it in the results (it should be at the top.)

☞ In the Finder, select Go ▹ Utilities from the menu bar, or press the key combination shift-command-U. The application is in the folder that opens.

☞ Open LaunchPad. Click Utilities, then Console in the icon grid.

Make sure the title of the Console window is All Messages. If it isn't, select All Messages from the SYSTEM LOG QUERIES menu on the left. If you don't see that menu, select

View ▹ Show Log List

from the menu bar.

Scroll back in the log to the time you noted above. Select any messages timestamped from then until the end of the episode. Copy them to the Clipboard (command-C). Paste into a reply to this message (command-V).

When posting a log extract, be selective. In most cases, a few dozen lines are more than enough.

Please do not indiscriminately dump thousands of lines from the log into this discussion.

Important: Some private information, such as your name, may appear in the log. Anonymize before posting.

I'm curious, what has trasnpired since you posted this? Have you been able to make any headway on finding out the cause? I think the same problem has caused a corruption of my Time Machine data.

Thanks in advance

I've been following this issue for a long time on one of the other Apple forum discussions. A suggestion was made to install an app called Jettison (by St. Clair Software). Since doing this two days ago, I have not seen the infamous "improper ejection" error message. Jettison seems to do, automatically without any effort on my part, exactly what the developer says: "Jettison eliminates the hassle of manually ejecting external drives before you put your MacBook to sleep and remounting them when it wakes."

By automatically unmounting my two external USB drives when the computer goes to sleep, Jettison is eliminating the opportunity for Apple's faulty USB power management system to improperly eject my external drives. As soon as my computer wakes up, Jettison quickly remounts the external drives. And, most importantly, Jettison has NOT caused any conflict with my Time Machine backups or my SuperDuper clone backups (three of which are scheduled to run automatically at 1:00am every night.

See: <http://stclairsoft.com/Jettison/index.html>

Modern Pixel wrote:

jimchik2,

Incidentally, the person I spoke to at OWC (where I purchased the drive) said that the Oxford 944SE chipset is known to have problems with sleeping and waking in certain situations. So, if any of your attached drives use that chipset, it could be the problem.

It is but it isn't the chipset. Meaning, those chips never had a problem prior to OS 10.9. I purchased 2 OWC Merury Elite Pro drive enclosures in Decemer 2015 and found that on my iMac11,1 running El Capitan, the drives only Sleep with the USB cable but never Sleep (unless Ejected) with the faster (on my computer anyway) FW800 cable. Here's what OWC told me, and I quote:

"This is a known issue with both the Oxford 944 and JMicron 355 chipset in 10.9 or later. Unfortunately, we have not received a fix for the issue from Oxford or JMicron. We've also submitted a bug report to Apple and have not heard back from them either."