Unable to mount external hard drive

I think I've found/corrected the issue! (I was getting the same exact error # as you - with a brand new, never used 5TB LaCie Mobile drive)...

First Aid did not work for me.

In Disc utility, click on the disk2k2 image, navigate to 'Partition' and under the Format dropdown, there are several options. Mine was set to the bottom choice ('Mac OS Extended' I think?) So I looked up what some of the other ones meant (they're all acronyms with descriptions that don't resonate with me) so I selected on 'APFS' as the best one for me (running 10.15.5 on a 2015 MacBook Pro)... Create the Partition (mine was for the entire 5TB since there was nothing else on it) - it runs the process by un mounting/erasing/re mounting the drive and BOOM - it now works.

After doing this, I assigned it to Time Machine as the preferred disc. It erased it and reformatted it in whatever way it needed to run my time machine backups.

CireT Said:

"Unable to mount external hard drive: I have a MacBook Air (Retina, 13-inch, 2018) running MacOS Catalina 10.15.4. While I connect an external USB hard drive, the MacBook Air does not mount it.[...]"

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A Few Thoughts:

• Reset the SMC and NVRAM:

Sometimes changes are made to the system (i.e. updates) and then system settings (i.e. for Ports) become manipulated, technically. So try resetting the SMC and NVRAM on your Mac.

• Plug into enter Device:

Have you plugged this into another Mac? Have you plugged this into a Windows PC?

• Any Security Software:

Security Software may be not letting this to Mount, due to Firewall settings. So, uninstall it (using the uninstaller from the developer). Security Software just gets in the way on a Mac, and this is a pure example as to why and how.

• Try Another User:

Create a new Administrator User, and log into it, seeing if you can connect it and access this Hard Drive. If so, it is likely an issue with your current user?

• Scan with Malwarebytes for Mac:

Start with running a scan for malware, using Malwarebytes for Mac and remove what is found. Perhaps something was installed that made this occur. Remove what is found from the quarantine. Malware is short for: Malicious Software, which makes you computer act in a mislead manor.

Downloads:

1. Malwarebytes Anti-Malware for Mac
2. Malwarebytes Uninstaller

Thanks for reaching out to the Apple Support Communities, CireT!

It sounds like you’re having an issue mounting an external drive to your Mac. I suggest starting with these steps to Repair a storage device in Disk Utility on Mac. You’re on the right track by wanting to repair the storage and this article will give you the steps you should take.

I also recommend taking a look at this article with steps to follow for How to use safe mode on your Mac. This will perform checks and stop certain software from starting up automatically. Once you are in safe mode, test to see if you have the same issue.

Let me know if you continue to have issues and have a super day!

Got a similar issue. However, my drive still mounts but the error makes me feel uncomfortable.

DiskUtility doesn’t fix it, warns, still exits with 0.

It seems fsck for apfs is mostly decorative, as I have yet to encounter a SINGLE problem it reports that it actually can fix.

As you say, reformatting a drive with (in my case) 8TB of data isn’t an option, particularly when we’re talking about a brand new, freshly formatted drive, and 8TB of data backed up with CCC from a laptop and backup drive...