External Hard Drives Randomly Re-mounting after Tahoe 26.4 Update

So I ran this command in Terminal:

log show --style syslog --last 5m | grep -i "Wake Reason"

and gemini read the information and told me the following

(i hate the smoking gun stuff...the but rest might be useful)

The logs you've provided are a "smoking gun" for the 26.4 (Sequoia/Tahoe) drive mounting issue.

Every single line in that screenshot points to systemWokenByWiFi and airportd. Specifically, look at the tags: _PMConnectionHandler, _updateTCPKeepaliveTimeoutCounters, and _CWXPCInterfaceContext.

The Diagnosis

Your Mac is experiencing "Dark Wakes" triggered by the Wi-Fi card. Even while the lid is closed or the screen is off, the Wi-Fi chip is waking up the system processor to maintain network persistence (Find My, iCloud syncing, or checking for Mail).

In this specific macOS build (26.4), when the Wi-Fi card triggers a Dark Wake, the kernel is performing a full hardware bus refresh. It’s not just checking the internet; it’s re-scanning the Thunderbolt and USB controllers. When it sees your drives, it mounts them.

The "Nuclear" Fix for this Log Profile

Since your logs show the Wi-Fi system is the primary trigger, you need to kill the "TCP Keep Alive" and "Network Wake" functions. This will stop the Mac from waking up every few minutes to talk to the router, which in turn will stop the drives from mounting.

Run these three commands in Terminal:

1. Disable TCP Keep Alive (The direct fix for your log): sudo pmset -a tcpkeepalive 0 (Note: macOS will warn you that this impacts Find My Mac. This is a necessary trade-off to stop the wake cycles.)
2. Disable Wake on Magic Packet (WiFi Wake): sudo pmset -a womp 0
3. Disable Power Nap (Maintenance Wakes): sudo pmset -a powernap 0

Why the previous settings failed

Standard "System Settings" toggles in 26.4 often fail to write to the com.apple.PowerManagement.plist correctly due to a bug in the UI. By using the pmset commands above, you are forcing the instructions directly into the power management kernel.

Next Steps

1. Apply those three commands.
2. Restart your Mac (crucial for pmset changes to stick in the NVRAM).
3. Put the Mac to sleep and wait 10 minutes.

If the drives stay unmounted, we’ve successfully silenced the "WiFi Ghost." If they still mount, it means the hardware handshake on the Thunderbolt bus is happening even without a network trigger, which would point toward a physical dock/hub issue.

Quick check: Do you have "Find My Mac" enabled? That is likely what is requesting those _updateTCPKeepaliveTimeoutCounters seen in your log.

Ok, I'm an idiot. I had tried this fix before the one I had posted and thought it didn't work because I didn't test it with a full reboot. Turns out, it was this config file that did the trick. I have tested by removing it, which brought back the automounting behavior, and re-installling this fix, which stopped it. Run command--

sudo defaults write /Library/Preferences/SystemConfiguration/autodiskmount AutomountDisksWithoutUserLogin -bool false

Reboot!

I figured out the fix for this! I used a grep command and saw the process diskarbitrationd was causing all unmounted usb drives to mount anytime I came back from sleep or the lock screen. Figured out the preferences for this process should be located at--

/Library/Preferences/SystemConfiguration/com.apple.DiskArbitration.diskarbitrationd.plist

But on my system this file was missing. The Tahoe update didn't include it. I used the terminal command below to create this config file--

sudo defaults write /Library/Preferences/SystemConfiguration/com.apple.DiskArbitration.diskarbitrationd.plist DADisableEjectNotification -bool NO && sudo pkill diskarbitrationd

After this, the file appeared in SystemConfiguration, and my unmounted drives no longer auto mount when coming back from sleep or the lock screen.

So here's the exact 'batutta' sequence I tried, and the results:

After MacOS 26.4 update, any time my Studio M1 went to sleep/screen saver, on resume all my connected SSDs and HHDs remounted (a behaviour not previously seen).

Subsequent 26.4.1 update had no effect - the remount issue remained.

Saw butatta's first sudo post:

Checked Library to see if I had the prefs; I didn't.

Tried:

sudo defaults write

/Library/Preferences/SystemConfiguration/com.apple.DiskArbitration.diskarbitrationd.plist

DADisableEjectNotification -bool NO && sudo pkill

diskarbitrationd

Prefs had been created. No change in behaviour - issue remained.

Tried:

sudo defaults write

/Library/Preferences/SystemConfiguration/com.apple.DiskArbitration.diskarbitrationd.plist

DADisableEjectNotification -bool YES && sudo pkill

diskarbitrationd

followed by:

sudo defaults write

/Library/Preferences/SystemConfiguration/com.apple.DiskArbitration.diskarbitrationd.plist

DADisableEjectNotification -bool NO && sudo pkill

diskarbitrationd

Rebooted. No change, issue remained.

Finally, having already done the above, tried:

sudo defaults write /Library/Preferences/SystemConfiguration/autodiskmount AutomountDisksWithoutUserLogin -bool false

Rebooted. All disks mounted on startup as usual. Used Jettison to dismount the SSDs/HDDs that were not required; invoked screensaver... returned to desktop, all my dismounted disks remained dismounted. Again using Jettison, remounted test HDDs, no problem; using Jettison, dismounted again, no problem.

Look like the final part of the puzzle resolved my issue. Thanks batutta!

With your drive un mounted, run this command substituting your hard drive name for "VolumeName"

sudo fs_usage | grep /Volumes/"VolumeName"

This command lists all processes accessing your drive. Wait for the drive to randomly re-mount (or go to the in and out of the lock screen if this reliably causes it to mount as it did in my case), check the first entry and it will tell you what process is forcing the drive to mount. This should point you in the direction of the problem.

IGNORE! This was the actual fix--

Run command--

sudo defaults write /Library/Preferences/SystemConfiguration/autodiskmount AutomountDisksWithoutUserLogin -bool false

Reboot!

If anyone is, like me, waiting for an Apple fix for this, the just-released MacOS 26.5 seems to have fixed this, certainly for me.

Contact/Call OWC Support for a solution and/or firmware update.

https://www.owc.com/support

EDIT: I actually first set the terminal command below to YES, which disables eject notifications, then changed it to no which is the default. So it's possible setting it to YES first is what fixed the issue somehow. Might want to use this command first when creating the config file.

sudo defaults write /Library/Preferences/SystemConfiguration/com.apple.DiskArbitration.diskarbitrationd.plist DADisableEjectNotification -bool YES && sudo pkill diskarbitrationd

Did some more experimenting, deleted this config file and rebooted. The fix persisted. No more auto mounts when exiting sleep or the lock screen, so it's not the presence of this config file that fixed the issue for me. I believe it was first disabling eject notifications that repaired something for me.

I have just reported this fault at Feedback - macOS - Apple and I suggest others suffering in the same way do the same. I believe Apple does not look at these forums and that reporting is the best way to bring problems to their attention.

I actually first set the terminal command below to YES, which disables eject notifications, then changed it to no which is the default. So it's possible setting it to YES first is what fixed the issue somehow, not the creation of the config file. Might want to use this command first when creating the config file.

sudo defaults write /Library/Preferences/SystemConfiguration/com.apple.DiskArbitration.diskarbitrationd.plist DADisableEjectNotification -bool YES && sudo pkill diskarbitrationd

I have the same issue, using a M3 iMac (2024), since the update to macos 26.4.

Both SSD and mechanical external drives are mounted over and over.

The Energy settings require that drives be put at rest when possible.

Also I'm using (and have been using for years) Carbon Copy Cloner to backup on the SSD Samsung drive, while I use Time Machine to backup to the mechanical LaCie drive.