External "Disk Not Ejected Properly" on M1 MBP issue, SOLVED (for me)

[Rod]

This is becoming a bit of an old chestnut; "Disk Not Ejected Properly"...there are so many online articles about this persistant problem suggesting such fixes as reformatting your EHD, replacing your cables, resetting SMC/NVRAM, using a powered hub even reinstalling macOS.

I have to admit I was feeling a bit smug about this topic as it had never cropped up as a problem for me, until now. My wife updated her 2018 MBP 500GB to a 2023 M2 MBA 1TB so our partitioned Samsung T5 SSD 2TB backup drive was no longer large enough for us both.

I decided to buy myself a similar 2TB drive for my CCC backups and dedicate the Samsung to my wife for hers.
I chose a SanDisk Extreme 2TB Portable SSD which was perfect for my purposes partitioned into two equal halves one for CCC and the other for some excess apps but after setup and my first CCC backup I started getting the "Disk Not Ejected Properly" message after sleep. Interestingly as with other users the disk icons remained on the desktop and finder and could still be accessed in the normal way which indicated (to me) that it had effectively reconnected if indeed, it ever disconnected.

So, I scanned the web for an answer/solution only to find the previously mentioned suggestions and a Apple Support page which said it was being "Updated" check back soon.

This is a brand new disk, plugged in directly via USB-C port, I erased and formatted it as APFS prior to use but every time the MBP goes to sleep, on awakening I get the "Disk Not Ejected Properly" message. Worth noting; the Samsung T5 now connected to my wife's MBA via a USB hub does not do this. Yes, I did try the SanDisk with a USB hub too but the result was unfortunately the same.
So, I have to assume there is something different about the SanDisk.

Anyhow, this is what I did;
System Settings > Battery > Options > I turned on; Prevent automatic sleeping on power adaptor when display is off. I restarted just to be sure.
I thought this might be enough in itself to solve the problem but no. Next:
System Settings > Lock screen > Turn display off on power adaptor when inactive > changed to; Never. I didn't bother to change the same setting for battery power as I would not normally have the EHD connected on battery.
This did it. My screen saver still comes on after 20min (and remains on) as per my Power settings requiring login as per Security settings with the one down side being I now have to put the device to sleep manually (I use a Hot Corner) and after 2 days I've had no more "Disk Not Ejected Properly" messages. I've also found just closing the lid also works with this method.

I hope Apple come up with a more appropriate solution to this niggling issue. I do have a powered hub in Bali which may solve the problem but for the time being my problem is solved.
Hopefully with a similar M series device running Sonoma this will work for you too but obviously different macOS and desktop devices may have different settings options/menus.

 

[Jimmysb]

I have 2 USB A SSDs plugged in, and have this issue on and off. Originally, overnight I could have up to 20 instances of the error, however, after an update these stopped, and now I get it occasionally, but always both drives. I was given (on this forum) all sorts of settings to change sleep/don't sleep etc, and none made any difference. The error usually happens over night, but I have had it whilst using my Mac.
I put it down to another apple anomaly, and live with it.

 

[MacInWin]

You can try Amphetemine, an app that will "tickle" drives to keep them awake. Drives that have a "sleep" function will trigger that warning.

 

[Rod]

@Jimmysb, to have it happening during use is odd. It was my impression that this occurs when the display goes off as part of Power Settings. From what I have read power to external devices goes off when the display goes off, unless otherwise set. Hence some have reported success with Amphetamine which prevents the HD from sleeping for any length of time. For others this has not worked either. I think it also has something to do with the EHD such as a "sleep" function mentioned by Jake above. It seems even the format of the EHD may make a difference for somel eg. APFS or MacOS Extended (Journalled).
So far my fix is working.

 

[Rod]

Update: I should have known this. After actually shutting down my MBP rather than just restarting I discovered that "System Settings > Battery > Options > Turn on; Prevent automatic sleeping on power adaptor when display is off." now works, as I'd expected, on its own without changing the "Display off" setting to "Never". Now screen saver and sleep functions work as before and the SanDisk does not eject.
So, as said, I should have known, Restart and Shutdown are not the same thing especially when it comes to System Settings.

 

[MacBiter]

So, as said, I should have known, Restart and Shutdown are not the same thing especially when it comes to System Settings.

Yes - on the rare occasions I have to do a hard Shut Down, when I reboot I first do a soft Shut Down, then a Restart.