Since MacOS 15.4 or 15.4.1 the external disks (via TerraMaster D4-320) attached to my M1 MacBookPro either don’t mount after rebooting, or if they do mount they get ejected as soon as the lid is closed. I can’t tell if this a:
When it’s not mounted the disks don’t even show up under DiskUtility. How would you go about troubleshooting?
I had a problem with disks unmounting, and disabling “Put hard disks to sleep when possible” in System Settings->Energy fixed it.
I have a brand new Synology, my first NAS. I set a long copy going from old hard drives to the Synology volume and sometimes when I return later and unlock the computer, the copy has failed. Seemingly because the volume has unmounted.
Thanks, I have seen the same advice elsewhere. Yet I can’t find that option. Instead I see:
I’ve searched system settings for: Sleep, Disk, … and just about everything in between.
On the off chance that the poorly worded, “Prevent automatic sleeping on power adapter when the
display is off” - I’ve even enable that.
Wish me luck.
@zkarj I would almost be happy if I had that problem. At least it would be doing something.
EDIT #1 - Now that the disks are reattached the option to never put disks to sleep appears. Funny apple is supposed to be good at usability. Not this time.
It looks like that setting isn’t available on MacBooks. I have it disabled on my Mini but can’t find it on my MacBook Pro. Ugh 
It turns out the setting is only visible when the disks are plugged in and enabled. I’m my case, I had to shutdown both the Mac and the external drive bay. Then start both, get hit by a permissions dialog, then option appeared.
Poor usability from Apple.
I’m glad you found that and I hope that it keeps the drives mounted
