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External SSD formatting problem

Hi everyone,

I recently bought a MacBook Pro M1 and a SanDisk external ssd. The ssd was working very well at first. I could erase, reformat etc. . I tried also other formatting types and there were no problems. But I wanted to partition my ssd. First I partitioned into two Mac OS extended parts. Then, I partitioned it into 3 parts (2 of them Mac OS extended, 1 ExFat). This operation failed. Then it began to fail.


I could not erase the disk. It always showed an error. I erased from a Windows PC then initialized on the Mac and tried again. It worked well once but then, there were problems while reading and writing. Now I cannot erase the disk. Also cannot use it. It always shows the errors shown below. Also first aid shows the errors shown. How can I fix these errors?


Thank you very much.


ERRORS: (Sorry, I could not upload the screenshots due to storage limit)


  • When I try to write, read data or expand zip files inside the ssd, it shows the error: "Error identifying a writable temporary folder. Try moving the archive to another volume"
  • When I try to move an app to the ssd, it says: "The operation can't be completed because an unexpected error occurred (error code -50)"
  • When I try to erase the whole disk, it shows: "The volume on disk4 couldn't be unmounted because it is in use by process 0 (kernel). Couldn't unmount disk. (-69888)"
  • When I try to eject it, a warning shows up saying that it is in use and asks me whether I want to force eject.
  • When I try first aid on the whole disk, it says: "Problems were found with the partition map which might prevent booting"
  • When I try first aid on the volume named 'External SSD'' it says: "Volume could not be unmounted"


When I list the disks on terminal it shows my ssd:









Posted on Jul 18, 2021 10:41 AM

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Question marked as Top-ranking reply

Posted on Jul 19, 2021 6:08 PM

Throughout the day I've tried many things. But finally I solved it by first restarting the Mac, then formatting my external ssd on a Windows PC to exFAT with aus 128 kb. Then I inserted my ssd to my Mac and used first aid before erasing the ssd. Then I erased it into exFAT format (GUID). Now, it works fine. I tried many things so, I do not know where exactly the problem was but this process fixed it.

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3 replies
Question marked as Top-ranking reply

Jul 19, 2021 6:08 PM in response to kaanatak

Throughout the day I've tried many things. But finally I solved it by first restarting the Mac, then formatting my external ssd on a Windows PC to exFAT with aus 128 kb. Then I inserted my ssd to my Mac and used first aid before erasing the ssd. Then I erased it into exFAT format (GUID). Now, it works fine. I tried many things so, I do not know where exactly the problem was but this process fixed it.

Jul 18, 2021 11:28 AM in response to kaanatak

kaanatak wrote:

Hi everyone,
I recently bought a MacBook Pro M1 and a SanDisk external ssd. The ssd was working very well at first. I could erase, reformat etc. . I tried also other formatting types and there were no problems. But I wanted to partition my ssd. First I partitioned into two Mac OS extended parts. Then, I partitioned it into 3 parts (2 of them Mac OS extended, 1 ExFat). This operation failed. Then it began to fail.

I could not erase the disk. It always showed an error. I erased from a Windows PC then initialized on the Mac and tried again. It worked well once but then, there were problems while reading and writing. Now I cannot erase the disk. Also cannot use it. It always shows the errors shown below. Also first aid shows the errors shown. How can I fix these errors?

Thank you very much.

ERRORS: (Sorry, I could not upload the screenshots due to storage limit)

When I try to write, read data or expand zip files inside the ssd, it shows the error: • "Error identifying a writable temporary folder. Try moving the archive to another volume"
When I try to move an app to the ssd, it says: • "The operation can't be completed because an unexpected error occurred (error code -50)"
When I try to erase the whole disk, it shows: • "The volume on disk4 couldn't be unmounted because it is in use by process 0 (kernel). Couldn't unmount disk. (-69888)"
• When I try to eject it, a warning shows up saying that it is in use and asks me whether I want to force eject.
When I try first aid on the whole disk, it says: • "Problems were found with the partition map which might prevent booting"
When I try first aid on the volume named 'External SSD'' it says: • "Volume could not be unmounted"

When I list the disks on terminal it shows my ssd:
https://discussions.apple.com/content/attachment/5d727eb0-9f56-4b28-b6f0-7c33b8848cc9


GUID/apfs


Erase and reformat a storage device in Disk Utility on Mac

https://support.apple.com/guide/disk-utility/erase-and-reformat-a-storage-device-dskutl14079/20.0/mac/11.0



Format a disk for Windows computers in Disk Utility on Mac ...


External SSD formatting problem

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