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External disk (2 TB Seagate) is captured by fsck when plugged into a USB 3.0 port on my Macbook Pro (macOS Mojave 10.14.5). This has been discussed by @ArielAllon, and indeed, when I kill the fsck process, the disk is immediately mounted and I can see and read it. When I eject the disk and plug it in again, I always have to kill fsck. I have left fsck running for 12 hours and it never completes. When I kill it, a pop-up warns that the disk could not be repaired.

My problem now, as Ariel mentioned, is that the disk is read-only, owned by root (or wheel?). I would like to use the remaining 150 GB on the disk, (remove old backups, etc) and prevent fsck from capturing it when attached. Thanks for any help...

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  • What is the physical interface for the disk? Just edit that into the question like I edited the tags, please.
    – bmike ♦
    Commented Jul 24, 2019 at 17:03
  • Relevant questions - apple.stackexchange.com/questions/268998/… and apple.stackexchange.com/questions/235309/…
    – Tetsujin
    Commented Jul 24, 2019 at 17:07
  • @bmike, I have edited the first sentence to state that the interface is USB direct to my Macbook
    – Ben
    Commented Jul 24, 2019 at 19:38
  • Thanks for the helpful edit, I doubt the linked questions above will help, but they are good reading. I’ve answered, but you might need to take that drive to another OS or specialized tool to salvage / copy data off and then try wiping it.
    – bmike ♦
    Commented Jul 25, 2019 at 2:10

3 Answers 3

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The two items that come to mind are getting software that can try and repair the disk structure and prevent the mounting like Disk Warrior or connecting the drive using a USB write blocker / forensic adapter so that the disk just presents as read-only so you can get any data off it.

Then, you would wipe the drive if you can’t get it sorted. The native tool will choke on fsck even if you disable the automatic check when it comes time to mount the drive normally.

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I used to frequently have that problem of waiting for a long time for a USB hard disk to mount while waiting for fsck to complete - due to a defective USB cable that occasionally disconnect the disk.

Clean Unmount

I have made it a habit to manually unmount the disk from command line

hdiutil eject disk2

Prevent fsck From Checking

From https://apple.stackexchange.com/a/230712/57733, first get the UUID of the external disk with diskutil list, then edit /etc/fstab with the value

diskutil info /dev/diskXsY
sudo vifs
# Replace with the UUID of your disk
UUID=2FECDB7A-15F0-36F9-9A47-483B9669D6DC none exfat rw,auto 0 0

Or a more direct method is to rename the fsck link and binary

sudo mv /sbin/fsck_exfat /sbin/fsck_exfat.disabled
sudo mv  /System/Library/Filesystems/exfat.fs/Contents/Resources/fsck_exfat  /System/Library/Filesystems/exfat.fs/Contents/Resources/fsck_exfat.disabled
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  • 3
    Ok, the apple Disk Utility's first aid finally fixed the problem, where it had failed before. All is working now, I guess the lesson in this case was to be patient and give the disk utility several attempts to fix the disk even after failing. Thanks for your comments and suggestions - I will try them if/when this happens again.
    – Ben
    Commented Jul 25, 2019 at 2:47
  • Great news @ben so glad it worked. I was afraid you were toast.
    – bmike ♦
    Commented Jul 25, 2019 at 3:34
  • This is one of the most brutally painful experiences working on a mac system. I want to throw this out the window. This happened on several occasions. If something goes out, like an electrical outage, it can totally mess up an external drive that needs to be in exFat. It's brutal. I don't understand why this is still a problem, why this never got fixed. It's really really painful.
    – Paul Carlton
    Commented Mar 31, 2023 at 4:57
  • This check will occur everytime. Disabling fsck is the only option for now.
    – Ali Waqas
    Commented Mar 30 at 17:53
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I killed the fsck_hfs process with killall and the disk became available to do as I pleased.

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