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Why Is My Mac Hanging When Copying Files After Upgrading to macOS Catalina 10.15.4?

Frustrated man in front of a computer

UPDATE: This issue was fixed in macOS 10.15.5


Hearing From Our Customers

Are you working on a movie set, transferring hundreds of gigabytes from a camera card to a RAID array? Are you a photographer trying to copy a large project from one volume to another?

If so, you may have already encountered hangs copying files after you upgraded to macOS 10.15.4. When you encounter the hang we are discussing, you can still move your mouse but are no longer able to copy files.

Investigating the Hang

A few days after the macOS 10.15 update was released, we began to hear of “Finder hangs” from DITs (Digital Imaging Technician) on movie sets. They were having their Macs stall when transferring hundreds of gigabytes of video from their 4K and 8K camera cards to their OWC ThunderBlades and ThunderBays. Anytime we hear about this type of problem, we immediately start looking for a cause.

A day later, we were able to reproduce the problem 100% of the time by copying 300 GB of large (10 GB) files from one SoftRAID RAID volume to another. Using a kernel debugger, we determined that the hang was not caused by an error in the SoftRAID driver. We then were able to reproduce the hang on an AppleRAID volume, using the AJA System Test Lite test application.

Once we proved the hang was not a problem with the SoftRAID driver, we alerted Apple engineers to the issue and collected further information to help them with their investigation. I can’t say when Apple will release the fix for this problem, but in the past, when they have been alerted to a hang or kernel panic, they had it resolved in the next update to macOS.

We will update this blog post once we have confirmed that this hang has been fixed in a future release of macOS.

We Discovered a Temporary Work-Around for macOS 10.15.4

If you want to prevent this hang, there is a setting in the computer’s NVRAM, which can be changed as a temporary fix. NVRAM settings are saved in a dedicated chip in your Mac and determines settings such as the audio volume your Mac starts from, the output volume for sound, and which, if any, debugging features are enabled. One of these debug features allows you to disable the part of macOS which is causing the hang. This could result in a 5 – 10% slower read and write performance but will prevent the hang from occurring.

Note: To enable this setting, you will have to disable SIP (System Integrity Protection). SIP is a feature of macOS which offers advanced protection from malware. By disabling SIP, you could be making your Mac more susceptible to malware infections.

The instructions at the bottom of this post show you how to revert NVRAM to the original (default) settings and how to re-enable SIP. I recommend that after you disable SIP and change the setting in NVRAM, you attach a sticky note to your monitor, reminding you to revert these changes once Apple fixes this problem.

Instructions for Preventing the Hang in macOS 10.15.4

Changing the NVRAM setting requires that you disable SIP.

Steps to Change NVRAM so That Hangs Are Prevented

Disable SIP:

  1. Restart the computer and then press the Command + R keys simultaneously, once you hear the startup chime. Keep holding the keys down until the Apple logo appears (this may take up to 90 seconds).
  2. When the menu bar says: “macOS Utilities,” you are booted into Recovery mode. Launch the Terminal application by selecting it from the Utilities menu.
  3. In the Terminal, type the following command:
    csrutil disable
  4. Afterward, the Terminal should display this message:
    Successfully disabled System Integrity Protection. Please restart...
  5. Select “Restart” from the Apple menu to restart your Mac.

Change the NVRAM Setting:

  1. In the Finder, select Utilities under the Go menu and then launch the Terminal application.
  2. In the Terminal window, type the following command:
    sudo nvram boot-args="dart=0"
  3. Restart your Mac normally, without any keys being pressed.
  4. To confirm that your NVRAM settings have been changed, relaunch the Terminal application and type the following command:
    nvram boot-args
  5. Check that the output from the command reads:
    boot-args dart=0

Instructions for Reverting Your Mac to a Normal Configuration

Once Apple releases an update to macOS 10.15, which fixes this issue, you can revert your Mac to the normal NVRAM settings and re-enable SIP.

Reset NVRAM to the default settings:

  1. In the Finder, select Utilities under the Go menu and then launch the Terminal application.
  2. In the Terminal window, type the following command:
    sudo nvram boot-args=
  3. Restart your Mac normally, without any keys being pressed.
  4. To confirm that your NVRAM settings have been changed, relaunch the Terminal application and type the following command:
    nvram boot-args
  5. Check that the output from the command reads:
    boot-args

Re-enable SIP:

  1. Restart the computer and then press the Command + R keys simultaneously, once you hear the startup chime. Keep holding the keys down until the Apple logo appears (this may take up to 90 seconds).
  2. When the menu bar says: “macOS Utilities,” you are booted into Recovery mode. Launch the Terminal application by selecting it from the Utilities menu.
  3. In the Terminal, type the following command:
    csrutil enable
  4. Afterward, the Terminal should display this message:
    Successfully enabled System Integrity Protection. Please restart...
  5. Select “Restart” from the Apple menu to restart your Mac.

UPDATES

Hang fixed in macOS 10.15.5

We have just finished testing with macOS 10.15.5 and have confirmed that this hang no longer occurs.

Hang also observed when copying to a server

Larry Jordan, the renowned creator of education material on video editing and post-production, contacted us after he encountered the same problem transferring a large amount of data from his iMac to a Synology server. He wrote about it in his latest weekly newsletter.

The NVRAM fix disables WiFi on some Macs

We have heard from numerous customers that the above change to NVRAM makes their WiFi networking no longer work. Users have reported this with MacBook Pros which contain T2 chips but it may affect addition Mac models.

If you encounter this problem, you can follow the steps above in the section “Instructions for Reverting Your Mac to a Normal Configuration.” You can then disable the Write Cache in the SoftRAID driver. This will prevent the hang from occurring but the write performance of your volume will be significantly decreased.

To disable the write cache in the SoftRAID driver:

  1. Launch the SoftRAID application.
  2. Select Preferences from the SoftRAID menu
  3. Select the RAID tab at the top of the Preferences window
  4. Unselect the checkbox next to “Enable write cache” so no checkmark appears in the box.
  5. Click the Save button at the bottom right of the Preferences window.
OWC Tim
the authorOWC Tim
Vice President of Software Engineering, Mac
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79 Comments

  • This is far too complicated for the average user….GEEKS at apple should have created this OS without this hangup….instead of fixing things that were not broken

  • I have an issue in 10.15.7 where it will just sit there in “Preparing to Copy” mode for almost two hours on only a few thousand files copied to the NAS. I can’t stop it without killing finder, and that makes connectivity to the NAS unstable.

    Have confirmed that I can mount the drives on the Catalina machine from a High Sierra box and copy them without issue to the same NAS. Don’t know if it’s related to this or to the ‘fix’ for this, but it’s made Catalina an entirely unusable OS for me.

  • Thank you, this solved my problem with the tedious time of preparing the copying of hundreds of photos and videos from my local MacBook to my server.
    Never would have thought it was a bug in Catalina. I had 10.15.3.

  • I recently installed ‘Pages’ version 10.3.5 (7029.5.5), from the Mac-store. Since then Copy & Paste text on ‘MS Word for Mac’ AND on ‘Pages’ will hang the system. I have to force-quit and re-open the programs, and back to square one. After much frustration & name-calling I tried ‘copying & pasting to a new ‘TextEdit’ file which I did without hanging-up, I then C&P from the ‘TextEdit file’ to “Pages’ and to ‘MS Word’ doc’s without hanging-up. Strange, indeed. [ I’m on mac OSx 10.15.6, Mac mini 16GB ram, 2.3 GHz Quad-Core Intel Core i7, (Late 2012)]…I have been with Mac since its inception…Where has all the Mac talent gone to ???

  • Sorry adding addition info. I am trying to copy files to the After Effects Extensions folder when it hangs.

    iMac (27-inch, Late 2013)
    3.2 GHz Quad-Core Intel Core i5
    32 GB 1600 MHz DDR3

    • If this problem is happening with macOS 10.15.7, it is not the same as the problem described in this blog post.

      My first step is always to perform a clean install of macOS to a new volume, and then repeat the test. If it works successfully, I start adding back my software solutions, one at a time, until I find the one which is causing the problem. This may seem like a lot of work but it is often the fastest way to discover the root cause.

      Good luck. I hope you find a resolution.

      Tim

  • Finder hang-up problem in Catalina 10.15.7

    I am having the problem of the Finder hanging up in OSX Catalina 10.15.7 while trying to move files. It is a late 2012 iMac with 3.2 GHz Quad-Core Intel Core i5 processor and a 1.2Gb Fusion drive. I have been running this version of Catalina for some time, but the problem started after I moved a number of very large files (folders with hundreds of photos and photos library packages) and iCloud is still catching up.

    I have run the disk utility first aid on all disk images but that did not help.

    Other apps like Folder Sync 2 are not showing any problems.

    In Finder, I can move one or two files once, but on subsequent attempts or if I try to move a lot, the finder hangs up the whole computer. I cannot relaunch The Finder with the CTRL-click option and cannot open Force Quit. I can force quit only by using the Activity Monitor if I remember to have it open and at least partly visible before the problem occurs; otherwise, I have to power off and reboot.

    • This sounds very frustrating.

      I have never been a fan of Fusion volumes. They work okay for small files, but seem to have problems when you are copying large numbers of files to or from them. I would suggest upgrading to a 2 TB SSD and replacing your fusion drive with single SSD instead. I think you will see much better performance and will have a more reliable solution as well.

      Tim

  • I am on 10.15.6 19G73 and transferring files to another Mac via Thunderbolt 3, and I am seeing the similar issues. The transfer is either interrupted so it would not finish, or the destination Mac will shut down during the transfer process.

    • I am not sure that this is the same issue as the one I described in this blog post. I assume you are using Target Disk Mode and not IP over Thunderbolt for this transfer. I am completely unfamiliar with the inner workings of Target Disk Mode, even thought it has been around since the days of FireWire 400. I expect that it is using a specific operating system built into the Macs firmware and not macOS that we know and love.

      I would try using a different cable between your two Macs. If that fails, you might try enabling IP over Thunderbolt as it will provide you a high speed connection between the two computers. (I believe this option is called “Thunderbolt Ethernet” in the Network pane of System Preferences.)

  • I started to get this issue on 10.15.5. I’ve now upgraded to 10.15.6 and i’m still suffering from finder hangs. If i leave my computer for about 1hr is seems to partially clear it, allowing me to view the finder and see apps on my desktop.
    I copied a large file to my apple iCloud folder (150gb). I think this is what triggered this.
    I’ve tried the workaround but they don’t clear the issue for me.

    • I think the issue you are encountering may be different than the one described in this blog post. I suggest you contact Apple for help regarding this issue or search Apple’s support forums to see if anyone else has experienced a similar problem.

      My guess, just a guess, is that your Finder hangs are due to the process which is uploading files in the background to iCloud. You can test this by disabling all your network connections (Network pane of System Preferences) and see if the hang goes away.

      Sorry I can’t be more helpful.

      • Hi Tim.
        Thanks for responding. I’ve switched off all connections but the hang still persists.
        I’m out of support with apple. Might have to be a fresh install. It only happened when I upgraded Catalina. Thinking i might give it a swerve going forward.

        • Without having your system in front of me, it is hard for me to determine what is going on.

          You could try using Activity Monitor, in the Utilities folder, to determine which applications or processes are performing lots of i/o.

          Open Activity Monitor and click on the Disk tab at the top of the main window. Make sure you have All Processes selected under the View menu or you might not see the application or process which is causing the slowdown.

          My guess is that there is one process which is making your Mac run slowly. It might be MDS, the process responsible for reindexing content to allow Spotlight searches.

          I hope you are able to figure this out.

          Tim

          • Thanks again Tim for the advice. I will take a look at the activity monitor to check there isn’t anything hogging resources (still).
            I had a little play this morning. I logged out of my apple account and then back in. That seems to have sorted this issue for the most part.
            It might have been something to do with how the cloud was configured on my system (to sync) as when I logged back in, the configuration of my files and folders that sync withy the cloud are now different.
            The main thing is, the finder isn’t hanging now.

            Many thanks! :)

          • Thanks Tim. Off the back of your suggestion to close network connections. I thought I would try signing out of my Apple account. This seems to have resolved the conflict (whatever was causing it.
            Many thanks

  • I’m on 10.15.5 and I’m experiencing this hang still. I’m a wedding photographer and need to back up thousands of raw files at a time. It freezes and never comes back. I have yet to get it to work, even attempting an Automator task. I tried the suggestions in the post and that didn’t fix it either. Any thoughts? This is an issue new to me with Catalina.

  • I still seem to have this problem between 10.15.5 and my Synology NAS 918+.

    After I mount the Synology Share using SMB, I open my network folder containing multiple project folders, i.e. Project A, Project B, Project C etc. I click on Project A and in there are 10,000 JPG’s. The folder takes a good 1-2 minutes to open. After it has loaded (none of the thumbnails load), I can only really view it in List View.

    I open a Local Folder on my Mac, containing an additional 2,000 images I want to add.

    I CMD+A to highlight them all and drag them from the Local folder across to the Network share folder containing the 10,000 images. This is when the Mac starts “Preparing to Copy”.

    What I have noticed here is that in the past it would do this really quickly with hundreds of “Grey” Temp files appearing almost instantly before it then starts to copy. Now since 10.15.4, it is producing maybe 1 file every 30 – 45 seconds, therefore 2k files will never work.

    Interestingly, if I go one folder level up on the Synology network share to where the group folders are – i.e. Project A, Project B, Project C. And simply copy the whole folder containing the 2,000 images as a folder to that area, the copy starts almost instantly and only takes a few minutes (50mb/s – 80mb/s).

    I then have to log into DSM, navigate to that folder using File Station and manually copy the files.

    This is odd behaviour as this never happened in the past.