MacOS thinks partition has different format and wont read/mount it

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Level 1

4 points

MacOS thinks partition has different format and wont read/mount it

I have an external SSD which used to have multiple partitions. Last night I was formatting some partitions for other uses and nothing happened to my other main partitions.

This morning a partition was no longer supported by Catalina 10.15.7 on my MacBook Pro 13 2017.

My partition is disk2s2, used to be formatted in exFAT for compatibility, and it's using GPT.

Diskutil cannot fix it with first aid.

Diskutil:

/dev/disk2 (external, physical):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *1.0 TB     disk2
   1:                        EFI EFI                     209.7 MB   disk2s1
   2: FFFFFFFF-FFFF-FFFF-FFFF-FFFFFFFFFFFF               500.0 GB   disk2s2
   3:           Linux Filesystem                         250.0 GB   disk2s3
   4:                 Apple_APFS Container disk3         250.0 GB   disk2s4

fdisk:

Disk: /dev/disk2	geometry: 121601/255/63 [1953525168 sectors]
Signature: 0xAA55
         Starting       Ending
 #: id  cyl  hd sec -  cyl  hd sec [     start -       size]
------------------------------------------------------------------------
 1: EE 1023 254  63 - 1023 254  63 [         1 - 1953525167] <Unknown ID>
 2: 00    0   0   0 -    0   0   0 [         0 -          0] unused
 3: 00    0   0   0 -    0   0   0 [         0 -          0] unused
 4: 00    0   0   0 -    0   0   0 [         0 -          0] unused

Disk: /dev/disk2s2	geometry: 60787/255/63 [976556032 sectors]
Signature: 0xAA55
         Starting       Ending
 #: id  cyl  hd sec -  cyl  hd sec [     start -       size]
------------------------------------------------------------------------
 1: F4 1012 244  52 - 1012 244  52 [4109694196 - 4109694196] SpeedStor
 2: F4 1012 244  52 - 1012 244  52 [4109694196 - 4109694196] SpeedStor
 3: F4 1012 244  52 - 1012 244  52 [4109694196 - 4109694196] SpeedStor
 4: F4 1012 244  52 - 1012 244  52 [4109694196 - 4109694196] SpeedStor

GPT show:

start        size  index  contents
           0           1         PMBR
           1           1         Pri GPT header
           2          32         Pri GPT table
          34           6
          40      409600      1  GPT part - C12A7328-F81F-11D2-BA4B-00A0C93EC93B
      409640        2008
      411648   976556032      2  GPT part - FFFFFFFF-FFFF-FFFF-FFFF-FFFFFFFFFFFF
   976967680        2048
   976969728   488275968      3  GPT part - 0FC63DAF-8483-4772-8E79-3D69D8477DE4
  1465245696        1056
  1465246752   488278376      4  GPT part - 7C3457EF-0000-11AA-AA11-00306543ECAC
  1953525128           7
  1953525135          32         Sec GPT table
  1953525167           1         Sec GPT header

Windows cannot open it either, and it doesn't give me any options to interact with.

I used a software for windows called Active Partition Recovery, and it seems that it recognizes the partition as exFAT, and it doesn't believe it is damaged. All the GPT data, tables look right. It also cannot recover it because "it exists as a live logical drive and the partition table contains the partition information".

I also used EaseUS Partition Master on Windows, and it will see the partition as "Other". It can't work with it in any way. Using this software I deleted the other 2 partitions I had, and now I have my partition and empty space on the ssd.

New diskutil:

/dev/disk2 (external, physical):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *1.0 TB     disk2
   1:           Windows Recovery                         500.0 GB   disk2s1

Fdisk is the same.

New GPT show.

start        size  index  contents
           0           1         PMBR
           1           1         Pri GPT header
           2          32         Pri GPT table
          34      411614
      411648   976556032      1  GPT part - DE94BBA4-06D1-4D40-A16A-BFD50179D6AC
   976967680   976557455
  1953525135          32         Sec GPT table
  1953525167           1         Sec GPT header

Before all of this, the SSD will only show the other partitions. Now when I plug it in with only the exFAT partition I get the error "The disk you inserted was not readable by this computer." which didn't show before.

Running first aid will show:

Running First Aid on “Samsung Portable SSD T5 Media” (disk2)

Checking prerequisites
Checking the partition list
Problems were found with the partition map, which might prevent booting
Partition map check failed because no slices were found. : (-69770)

Operation failed…

The data is there. These recovery programs see it, but they are all useless. I don't want to recover every file and lose the folder hierarchy, so I want to somehow fix this reading problem...

MacBook Pro 13″, macOS 10.15

Posted on Jan 31, 2021 12:59 PM

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Answer 1

Top-ranking reply

YooCata Author

Level 1

4 points

Feb 3, 2021 6:28 AM in response to YooCata

I solved my problem using this article:

https://www.transscendsurvival.org/2019/02/27/mac-osx-fixing-gpt-and-pmbr-tables/

However, first of all, what I have done. I formatted another USB stick to exFAT on MacOS just to have a point of reference. THANK YOU HWTech for the suggestion!

I opened windows and EaseUS Partition Master where I looked at my SSD and the new USB Stick. I saw that the USB stick has an EFI partition which I delete when my SSD started having problems. I thought that was only used for Linux as I had one installed on the ssd.

I copied the EFI partition from the new USB trick to the SSD. Windows was able to read my portion now and access all the files. This is when is start to backup stuff which wasn't already. MacOS still won't read it.

After I followed the link above and, BUT. At the step listed:

# index two (for me) is my data. We are going to use the default OSX / Mac HD partition values.

They used a default code which I didn't want to use because i wanted exFAT not Mac HD partition or whatever is that. So I called "gpt show disk3" which is the new USB stick and copied the code from there. This is the output for exFAT:

~ sudo gpt show disk3
Password:
     start      size  index  contents
         0         1         PMBR
         1         1         Pri GPT header
         2        32         Pri GPT table
        34         6
        40    409600      1  GPT part - C12A7328-F81F-11D2-BA4B-00A0C93EC93B
    409640      2008
    411648  15149056      2  GPT part - EBD0A0A2-B9E5-4433-87C0-68B6B72699C7
  15560704      1823
  15562527        32         Sec GPT table
  15562559         1         Sec GPT header

The code I used was : EBD0A0A2-B9E5-4433-87C0-68B6B72699C7

AGAIN: this is for the last GPT ADD in the link above.

All the steps I followed are bellow + the output from gpt show disk2:

sudo gpt -r show disk2
       start        size  index  contents
           0           1         PMBR
           1           1         Pri GPT header
           2          32         Pri GPT table
          34        2014
        2048      409600      1  GPT part - C12A7328-F81F-11D2-BA4B-00A0C93EC93B
      411648   976556032
   976967680   976556032      2  GPT part - DE94BBA4-06D1-4D40-A16A-BFD50179D6AC
  1953523712        1423
  1953525135          32         Sec GPT table
  1953525167           1         Sec GPT header


diskutil list (see what is your partition and disk)
sudo gpt -r show disk2 (for me is disk2 as its an external SSD)
diskutil unmountDisk disk2
sudo gpt destroy disk2
sudo gpt create -f disk2
sudo gpt add -b 2048 -i 1 -s 409600 -t C12A7328-F81F-11D2-BA4B-00A0C93EC93B disk2
(I copied the numbers above from "sudo gpt show disk2" NOT disk3) 
sudo gpt add -b 976967680 -i 2 -s 976556032 -t EBD0A0A2-B9E5-4433-87C0-68B6B72699C7 disk2
(This is the last step as I was describing above.)

Enjoy.

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Answer 2

HWTech

Level 9

60,284 points

Jan 31, 2021 6:11 PM in response to YooCata

It is dangerous and ill advised to use a Windows drive utility to make modifications to a drive used with macOS. macOS is much pickier about the layout of a drive than either Windows or Linux. Years ago when I started using Linux I was told you should only ever use the tools with the OS that owns the drive even if tools exist in the other OS because the tools in the other OS may not work exactly the same.

If this drive has important & unique data, then you should have frequent and regular backups of the external drive as well as your main boot drive. Formatting a partition is always risky.

You should start over by re-partitioning & formatting the drive as there may be other issues even if you are able to "repair" the partition table or file system. I personally would not trust things as they are without re-partitioning & formatting.

Unfortunately I don't know the codes used to identify the various partition types. I would have Disk Utility partition and format another drive with a GUID partition for exFAT (assuming Disk Utility created this external drive in the first place). Then I would use a Linux boot disk and use "fdisk" to read the type of partition type/ID associated with the exFAT partition. Then I would use "fdisk" to change the partition type on the broken drive to match. You will need to unmount & re-mount the drive for the changes to take affect so that the OS reloads the new modified partition table. Keep in mind it is very risky making changes to the original drive since it may cause other problems. It would be better to make a bit for bit clone and work from the clone so you don't cause more issues with the original drive.

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Answer 3

YooCata Author

Level 1

4 points

Feb 1, 2021 1:13 AM in response to HWTech

Thank you for your ideas! I find them very useful.

This drive was meant to be used across different operating systems thats why I went with exFAT. Would there be a better alternative?

Im going to attempt to work with your suggestion and come back with updates.

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Answer 4

HWTech

Level 9

60,284 points

Feb 1, 2021 8:43 AM in response to YooCata

YooCata wrote:

This drive was meant to be used across different operating systems thats why I went with exFAT. Would there be a better alternative?

exFAT is the preferred option for sharing a drive between macOS and Windows. You do need to have Disk Utility format the volume since Windows may use different allocation sizes that macOS may not recognize.

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Answer 5

YooCata Author

Level 1

4 points

Feb 3, 2021 6:31 AM in response to HWTech

Just wanted to say Thank you! for the suggestion to format another USB stick to exFAT as a point of reference. I was able to solve the problem by looking at that USB. You can see my solved solution with more info if you are interested.

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Answer 6

HWTech

Level 9

60,284 points

Feb 3, 2021 7:46 AM in response to YooCata

YooCata wrote:

I saw that the USB stick has an EFI partition which I delete when my SSD started having problems. I thought that was only used for Linux as I had one installed on the ssd.

FYI, if you need to remove the Linux bootloader all that is required is to remove the appropriate Linux folder from the ESP/EFI partition. For example many Linux distributions will name their bootloader folder after the distribution. For example Ubuntu will have a folder named "ubuntu" on the hidden EFI partition. Sometimes you may find just a generic "boot" folder. This generic boot folder is used because many systems firmware will only recognize the bootloader named "boot_x64.efi" contained within a folder named "boot" on the hidden EFI/ESP partition. Just deleting these folders will prevent Linux from booting on any UEFI system such as a Mac.

I'm glad you were able to sort it out.

Thanks for following up with the steps you used.

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MacOS thinks partition has different format and wont read/mount it

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