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In preparation for getting a new PC, I copied all my important files from my current PC's hard drive to a USB-connected hard drive. I let this process run overnight, and about an hour after it finished, my PC slowed to a crawl. Task manager showed 100% disk usage, which persisted over several power cycles, and the worst offender was "System", followed by "Antimalware Service Executable". "Settings > Windows security > Virus and threat protection" showed "Threat service has stopped. Restart it now." but would always fail to restart ("Unexpected error. Sorry, we ran into a problem. Please try again.")

After about 18 hours, I still had the same problem, despite my rudimentary troubleshooting attempts, so I decided to just reinstall windows using the built-in "Start fresh" utility. This fixed everything.

A few days later, I decided to make another copy of all my important files, this time to a USB flash drive. I ran it overnight, and this morning I again found that my disk usage was stuck at 100%. After a power cycle, the virus & threat protection service is stopped again, and fails to restart. I suspect this is not a coincidence. What might be causing this problem?

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  • I can (and do) copy 150 GB of machines from laptop to desktop about once a quarter. It takes about an hour and a half, throughput is steady, and there is no performance drop. Is Windows Defender finding either strange files or finding viruses? USB drive will be slower, but I can copy between USB drive and machine with no performance drop.
    – anon
    Commented May 2, 2021 at 18:58
  • Should be "takes about an hour (and a half) over wireless" 15 to 20 minutes over Ethernet.
    – anon
    Commented May 2, 2021 at 19:07
  • The performance drop while copying is reasonable and not really unexpected to me. The real problem comes after everything is done copying. What is the system doing? It's just using all my disk bandwidth for... what?
    – Edward
    Commented May 2, 2021 at 19:12
  • It appears virus and threat protection has revived itself... and it shows no viruses or issues (apart from wanting me to set up onedrive)
    – Edward
    Commented May 2, 2021 at 19:13
  • Once I have finished copying, there is nothing going on (Task Manager). Try to see what Windows Defender is doing.. It could be that WD is paying extra attention to the USB source of files
    – anon
    Commented May 2, 2021 at 19:13

1 Answer 1

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Try the Windows utility RoboCopy. Since RoboCopy uses direct disk I/O, it might be less apt to trigger the antimalware's inspection of each file as it's being copied.

You might be even better served making a disk image, rather than just copying specific files and folders. Tools such as Macrium Reflect Free can image a disk at speeds limited only by the HDD and USB speed. On an elderly laptop, I get ~80 to 100 megabytes/second, backing up a 100 GB drive in about 15 minutes. This backs up everything, even system files, and you can browse the image to access all files, even those inaccessible while your PC is running.

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  • I don't have the problematic laptop anymore, but I did recently use Reflect to duplicate 500GB of files on another PC with no issues. I will accept this answer to "close" the question.
    – Edward
    Commented Feb 10, 2023 at 15:01

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