Can't write to external hard drives after Big Sur 11.3.1 update

Argh! My computer updated to Big Sur 11.3.1 this morning and now I cannot write to my external hard drives, regardless of permission settings. Reading them works okay. I have ran First Aid on all the drives and no problems there; all are formatted to Mac OS Extended and mount just fine. I've done 'Get Info' on each drive, clicked the lock and entered my password to make changes, unchecked and rechecked 'ignore ownership on this volume' and all accounts are set to "read & write", however, it states "You can only read" underneath Sharing & Permissions. I can copy from without issue, but cannot copy to. Anyone else with the same issue? Yikes...

iMac Pro, macOS 11.3

Posted on May 16, 2021 2:13 PM

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Posted on May 16, 2021 2:16 PM

Boot into Safe Mode according to Start up your Mac in safe mode - Apple Support and see if the problem persists. Reboot normally and check again.


NOTE: Safe Mode boot can take up to 10 minutes as it's doing the following; 

• Verifies your startup disk and attempts to repair directory issues, if needed

• Loads only required kernel extensions (prevents 3rd party kernel/extensions from loading)

• Prevents Startup Items and Login Items from opening automatically

• Disables user-installed fonts 

• Deletes font caches, kernel cache, and other system cache files


7 replies
Question marked as Top-ranking reply

May 16, 2021 2:16 PM in response to kevinwstrick

Boot into Safe Mode according to Start up your Mac in safe mode - Apple Support and see if the problem persists. Reboot normally and check again.


NOTE: Safe Mode boot can take up to 10 minutes as it's doing the following; 

• Verifies your startup disk and attempts to repair directory issues, if needed

• Loads only required kernel extensions (prevents 3rd party kernel/extensions from loading)

• Prevents Startup Items and Login Items from opening automatically

• Disables user-installed fonts 

• Deletes font caches, kernel cache, and other system cache files


May 16, 2021 7:14 PM in response to Old Toad

Okay, it's been a few hours of trying various things and still am unable to write to an external hard drive. In short, Safe Boot did not work. In fact, I couldn't even get Safe Boot to work. I went and took a bath just to allow time for it to boot and all I got was a folder with a question mark that randomly flash on and off for an hour.


I also tried plugging in two thumb drives, one that is formatted in ExFat and the other Mac OS Extended. I can read and copy from the drives but cannot write anything to them. The drives also can't write anything to/from each other.


So here's the kicker: I have a new Mac laptop that's on Big Sur 11.2 and it also is having the same problem. Trying to do the same workarounds as stated above doesn't do anything to actually change the read/write capabilities.


One other thing that I think is involved with all this is that this software Cylance appeared randomly on both computers! Something to do with BlackBerry management I think, which is weird. I definitely didn't consciously install this and haven't opened up the laptop since last week. Both computers also have Rippling hard drive management software that is remotely controlled by my company so I think there's a clash in there somewhere. So I'll have to check with them to see if they know anything as well.

May 16, 2021 8:21 PM in response to kevinwstrick

kevinwstrick wrote:

One other thing that I think is involved with all this is that this software Cylance appeared randomly on both computers! Something to do with BlackBerry management I think, which is weird.

Cylance Smart Antivirus by BlackBerry is an antivirus/security package.


If your computers are managed remotely by your company, this could be the reason you're having issues. They could be blocking access as well as managing antivirus on your machines.


Definitely check with your company to see what's up.

May 17, 2021 9:37 AM in response to kevinwstrick

kevinwstrick wrote:

One other thing that I think is involved with all this is that this software Cylance appeared randomly on both computers!

First, there is no reason to ever install or run any 3rd party "cleaning", "optimizing", "speed-up", anti-virus, VPN or security apps on your Mac.  This user tip describes what you need to know and do in order to protect your Mac: Effective defenses against malware and other threats - Apple Community.  


There are no known viruses, i.e. self propagating, for Macs.  There are, however, adware and malware which require the user to install although unwittingly most of the time thru sneaky links, etc.   


Anti Virus developers try to group all types as viruses into their ad campaigns of fear.  They do a poor job of the detecting and isolating the adware and malware.  Since there are no viruses these apps use up a lot of system resources searching for what is non-existent and adversely affect system and app performance.


There is one app, Malwarebytes, which was developed by a long time contributor to these forums and a highly respected member of the computer security community, that is desshoigned solely to seek out adware and known malware and remove it.  The free version is more than adequate for most users.  


Also, unless you're using a true VPN tunnel, such as between you and your employer's or bank's servers, they are useless from a privacy standpoint: Public VPN's are anything but private.  


That being said uninstall Cylance according to the developer's instructions. Then you can check to see if you've removed all of the supporting files by downloading and running the shareware app Find Any File to search for any files with the application's or the developer's name in the file name.  For the Cylance software you'd do the following search(es): 


1 - Name contains cylance


Any files that are found can be dragged from the search results window to the Desktop or Trash bin in the Dock for deletion.


FAF can search areas that Spotlight can't like invisible folders, system folders and packages.  



May 17, 2021 10:47 AM in response to Old Toad

Hi all,

Following up here; I was in contact with my company's IT this morning and it turns out that my computers were on read-only access via Rippling, the tool my company uses to manage and encrypt computers and drives. Cylance is/was installed and managed via Rippling as well. I was put onto an 'except for' list and now everything is working again just as before. Phew!


Thank you to Old Toad and SerZak for taking the time to contribute solutions and help me out; it very much appreciated. Y'all rock and have a great week!

May 16, 2021 7:39 PM in response to kevinwstrick

Also, a couple other notes:

  • While Safe Boot didn't work on one machine (iMac Pro, Big Sur 11.3.1), it did work on the laptop (MacBook, Big Sur 11.2.3). Same result though; can read/copy from external, but cannot write to it.
  • I also have an alias folder "Relocated items.nosync" that is on the iMac's desktop, which I believe is the result of the install of 11.3.1

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Can't write to external hard drives after Big Sur 11.3.1 update

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