Sequoia 15.0 bugs - external hard drives

Sequoia update has caused mounting issues with external hard drives. Ex: had one working and then all of a sudden M3 Max MacBook Pro stops recognizing the device. Now, it won't even find it when it's plugged in. Device works fine on other devices.

Posted on Sep 26, 2024 10:10 AM

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Posted on Nov 13, 2024 8:11 PM

In my case, since I installed Sequoia, I can hardly ever eject any flash memory. It always tells me that I can't because they are in use by some other program. I have to force eject or shut down the laptop. With every upgrade I see Apple's quality and confidence drop a lot!

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Mar 29, 2025 10:35 PM in response to mtnman2152

Like many, I had this problem - my particular set up is as follows -


External Drive : OWC Aura P12 Pro PCIe 3.0 NVMe M.2 2280 SSD with 2x 4TB ram cards

Mac : Mac Studio M1 Ultra

OS : Sequoia 15.3.2

Had a Bad Idea and decided to clean up the major mess behind the big screen of tangled cables, USB hubs, power supplies, external drives, a mini Tardis machine etc etc - your basic horror show from plugging in every next device in, without ever rationalising any of it.

The OWC SSD had worked flawlessly since installation in June '23 - and just used any old generic thunderbolt cable to connect it and all worked fine.

After untangling and losing a *LOT* of excess and not often used gear, everything booted back up fine -

Until the Sequoia update ...

The OWC no longer appeared in either Finder or Disc Utility, which was weird because it had been a rock solid always there device for 1.5 years. Because there were no directories or files visible from the OWC could not use for backup or as an extension for big apps of the Mac's 1TB hard drive - a big drama!

For the same reason could not use the right click trick on any OWC files or folders in Finder, followed by Get Info / Sharing Permissions to alter the Permissions for the OWC.

Strange how often the basic 101 support solutions sometime work?

Changed the Thunderbolt cable between the Mac and the OWC to a "genuine" Apple Thunderbolt white job (not sure what it came with) and hey presto OWC + all folders and files appeared in both Finder and Disk Utility.

Apple are (inconsistently) picky about what, and for how long, 3rd party devices can be used with their gear, despite not making a whole bunch of external devices they know you will need over time (and they often sell those third party devices in their stores).

Morals -

      1. Keep a set of genuine apple cables around to test when you have a non connect issue (I know that 3rd party ones are often better made, cheaper and in more convenient lengths)
      2. Before upgrading any OS on any device, wait and search known issues before upgrading, especially compatibility and support issues.


Just feel a bit silly reporting such a simple fix .... cheers Max

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Apr 4, 2025 7:35 AM in response to mtnman2152

What I have been doing since this issue is:

  1. Plug the hard drive into an older mac I have (with Mojave in my case)
  2. Open terminal and run sudo pkill -f fsck
  3. Once the disk boots I run first aid in Disk Utility
  4. Then if I eject and plug onto the Sequoia, it boots as normal

Annoying but that's what's been my resolution so far until Apple does the right thing.


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Feb 3, 2025 11:51 AM in response to Maggot

Yes! I can verify that this IS a USB problem. Ever since I purchased a new external drive that has a USB hub and interfaces with my new MacbookPro M3 via USB 3.2 I have had issues with the drive not mounting. The drive mounts fine to my older MacbookPro with Intel chip. This is a 2-bay OWC expansion drive with an external power supply. Brand new. And again, it works/worked fine with the older, Intel-based MacbookPro.


In an effort to solve the problem, I upgraded the new MacbookPro to the latest version of Sonoma (it was running Sonoma, as was my Intel MacbookPro) and that seemed to solve the problem...the drive mounted. ONLY THIS LASTED JUST 3 DAYS and then it stopped again.


To make a long story short, I tried all of the safe boot, etc. suggestions and nothing worked. I ultimately (today) upgraded to Sequoia 15.3 figuring that if I took the machine into Apple, they'd demand that anyway. Still no go UNTIL I read this thread, and decided to try connecting the external drive to the MacbookPro via an old USB C to USB 3.0 cable plugged into a dongle that was then connected to the M3 Macbookpro...and IT WORKED. Drives mounted right up and a TimeMachine backup is running. System Info tells me that it believes that I have a USB 2.1 Hub Installed. (see image)



It of course remains to be seen if this continues to work (recall that I did have it working for a few days on Sonoma until it stopped...that was with a USB C 3.2 connection on the drive to USB C on the M3 Macbookpro connection). But there definitely seems to be something going on with this machine and its USB ports (yes, I tried all 3 ports earlier before the current "fix" and none of them allowed the drive to mount).


Downgrading to a USB 2.1 (or presumably older?) connection seems to work. FWIW.

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Feb 9, 2025 9:33 AM in response to mtnman2152

Apple! You have been my "rock" since the 1980's. My rear window carries the apple sticker because I've made a living off of my Apple computers.


I just turned 70...and purchased what may be my last Apple. A new 27" monitor, and a new iMac Studio with plenty of ram to run Adobe software, so I can continue to create graphics, and stay up to date with the OS.


The new iMac started glitching. Bright magenta screen, Adobe programs going blank, having to restart continually. My external used for Time Machine backup was full of older art files as well...so I also worked with an Apple specialist who after hours of investigating (which included re-installing the OS) realized my external was failing. I tried to mount the external to my 2017 iMac with Ventura OS, (which had worked fine for several years) and it will not mount.


However, my new iMac seems to be working fine since removing the external hard drive.


I chalked it up to the external failing. Did some investigating on recovery methods, and it most likely will need to be shipped out at great cost to get those older files off of it.


Last week I purchased a new SanDisk Extreme 2TB for Time Machine backups. It worked for 3 days. I checked it yesterday, and have a new message that says: The disk “My Backup” can’t be unlocked. A problem was detected with the disk that prevents it from being unlocked. Attached is a snapshot of the new external Disk First Aid check.


I have reached out to the Apple technician who is familiar with my former case, and am still waiting to hear from him.


Apple, please give us all an update on this BUG. Steve Jobs would not be happy right now. Neither am I. Apple is costing us money instead of making us money.

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Oct 3, 2024 11:33 PM in response to mtnman2152

I have a new external hard drive which is formatted in the format which only works on mac computers (I can't check what the format is as its not appearing in disk utility or finder)


Is the best option just to downgrade from Sequoia? or will an update be released quite quickly? I have very important data stored on this drive.

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Oct 7, 2024 7:44 AM in response to mtnman2152

My Time Machine external hard drive still works, but my three other external disks (Macintosh formatted disks) do not show up on my desktop or in disk utility. Spent hours on the phone with Apple support - tried most everything with no result. Booted up in safe mode, booted up in test user, restarted several times, disconnect and reconnect the disks, etc. No result. These disks worked fine before Sequoia. Naturally, the Apple technician said it was a hardware issue with the disks - very Microsoft of him. Suspect a software issue.

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Dec 17, 2024 2:18 PM in response to mtnman2152

My Time Machine drive got messed up. I think something happened when the the disk was attached and then crashed the computer. Luckily I was able to retrieve my files from a backup on the Time Machine from the week before. Sedona shows the disk but at this point the drive is unsafe to use. I will stick with Sedona until Mac fixes this problem. Nice to know I’m not the only one having these problems.

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Dec 19, 2024 1:45 PM in response to mtnman2152

Today, 12/19/24 online magazine 9to5Mac released an article about multiple (?) bugs in MacOS Sequoia 15.2 affecting Time Machine, Carbon Copy Cloner, SuperDuper! and possibly other backup utilities.


I use both Time Machine and CCC and can confirm the bugs are much, much older than Sequoia 15.2 (by years).


I suggest you read it. It’s called “MacOS Sequoia 15.2 Backup Bug(s)…” posted 12/19/2024. Good Luck and Merry Christmas!

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Jan 14, 2025 5:51 PM in response to mtnman2152

Same problem for me. Multiple older backup HDDs are not seen by the system, including Disk Utility. My backups are two weeks out of date, as of this message. For me the problem was not linked to an upgrade or a dot version OS update. I bought a new Mac Mini M4 in late November. External drives mounted fine, and both Time Machine and CCC ran normally. Sometime over the evening of Dec. 31, it all stopped. I had been on 15.1.1 for over a month, and was yet to update to 15.2. Why the failure happened without any evident change in the OS is a mystery. Having spent a fair bit on the Mini and monitor/peripherals, I am loath to buy backup disks, so this is missing piece is critical for me.

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Sequoia 15.0 bugs - external hard drives

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