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I've got external 3GB disk - that was formated under OSX, with partition (i guess exFat) so i could use it to move some data from my old windows 7 PC to Mac OSx I did it twice without problem, but after another session - Mac didn't saw the disk/partition, and when I put it back to windows PC, and windows automaticly tryed to repair it on startup...

In the meantime I realised - that on this disk there was also my archive of family photos from last years...

Everytime I put it in Windows, it try to convince me to format it, osx on the other hand ask for initialization... I didn't do any of these of course.

What I did allready:

  1. I’ve checked if the disk hasn't any bad sectors - and it seems to be completelly all right.

  2. Try to use First Aid on Mac - as I believed it could help - because partitioning was made on Mac. It didn't work:

    Running First Aid on “” (disk3s2)
    Repairing file system.
    Volume is already unmounted.
    Performing fsck_msdos -y /dev/rdisk3s2
    Invalid sector size: 0
    File system check exit code is 8.
    Restoring the original state found as unmounted.
    File system verify or repair failed. : (-69845)
    Operation failed…
    
  3. Checked it with TestDisk on Windows - which sugested, that there is GPT file system:

     1 P MS Reserved     34      262177      262144    [Microsoft reserved partition]
     1 P MS Reserved     34      262177      262144    [Microsoft reserved partition]
     2 P MS Data     264192      5860532223  5860268032    [Basic data partition]
    
  4. I also checked it with mac diskutil list- it confirmed that It is probably GPT with Microsoft main partition:

     $ diskutil list
     /dev/disk3 (external, physical):
     #:                       TYPE NAME                    SIZE       IDENTIFIER
     0:      GUID_partition_scheme                        *3.0 TB     disk3
     1:         Microsoft Reserved                         134.2 MB   disk3s1
     2:       Microsoft Basic Data                         3.0 TB     disk3s2
    
  5. I also get some information about this GPT using gpt show:

     $ sudo gpt -r show /dev/disk3
          start           size     index  contents
              0              1            PMBR
              1              1            Pri GPT header
              2             32            Pri GPT table
             34         262144         1  GPT part - E3C9E316-0B5C-4DB8-817D-F92DF00215AE
         262178           2014         
         264192     5860268032         2  GPT part - EBD0A0A2-B9E5-4433-87C0-68B6B72699C7
     5860532224            910         
     5860533134             32            Sec GPT table
     5860533166              1            Sec GPT header
    

As the files are precious to me I’m afraid of doing any further step. I know I should probably manually rebuilt this GPT

As suggested by David Anderson : sudo dd if=/dev/disk3s2 count=1 | hexdump -Cv gives:

   1+0 records in
   1+0 records out
   512 bytes transferred in 0.021839 secs (23444 bytes/sec)
   00000000  eb 76 90 45 58 46 41 54  20 20 20 00 00 00 00 00  |.v.EXFAT   .....|
   00000010  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
   00000020  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
   00000030  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
   00000040  00 08 04 00 00 00 00 00  00 98 4c 5d 01 00 00 00  |..........L]....|
   00000050  00 08 00 00 00 58 00 00  00 60 00 00 87 a9 2b 00  |.....X...`....+.|
   00000060  04 00 00 00 ed 38 5e 9c  00 01 02 00 09 0b 01 80  |.....8^.........|
   00000070  5b 00 00 00 00 00 00 00  33 c9 8e d1 8e c1 8e d9  |[.......3.......|
   00000080  bc d0 7b bd 00 7c 88 16  6f 7c b4 41 bb aa 55 cd  |..{..|..o|.A..U.|
   00000090  13 72 69 81 fb 55 aa 75  63 f6 c1 01 74 5e fe 06  |.ri..U.uc...t^..|
   000000a0  02 7c 66 50 b0 65 e8 a6  00 66 58 66 b8 01 00 00  |.|fP.e...fXf....|
   000000b0  00 8a 0e 6d 7c 66 d3 e0  66 89 46 e8 66 b8 01 00  |...m|f..f.F.f...|
   000000c0  00 00 8a 0e 6c 7c 66 d3  e0 66 89 46 d8 66 a1 40  |....l|f..f.F.f.@|
   000000d0  7c 66 40 bb 00 7e b9 01  00 66 50 e8 41 00 66 58  ||f@..~...fP.A.fX|
   000000e0  66 40 bb 00 80 b9 01 00  e8 34 00 66 50 b0 78 e8  |f@.......4.fP.x.|
   000000f0  5d 00 66 58 e9 09 01 a0  fc 7d eb 05 a0 fb 7d eb  |].fX.....}....}.|
   00000100  00 b4 7d 8b f0 ac 98 40  74 0c 48 74 0e b4 0e bb  |..}....@t.Ht....|
   00000110  07 00 cd 10 eb ef a0 fd  7d eb e6 cd 16 cd 19 66  |........}......f|
   00000120  60 66 6a 00 66 50 06 53  66 68 10 00 01 00 b4 42  |`fj.fP.Sfh.....B|
   00000130  b2 80 8a 16 6f 7c 8b f4  cd 13 66 58 66 58 66 58  |....o|....fXfXfX|
   00000140  66 58 66 61 72 b1 03 5e  d8 66 40 49 75 d1 c3 66  |fXfar..^.f@Iu..f|
   00000150  60 b4 0e bb 07 00 b9 01  00 cd 10 66 61 c3 42 00  |`..........fa.B.|
   00000160  4f 00 4f 00 54 00 4d 00  47 00 52 00 0d 0a 52 65  |O.O.T.M.G.R...Re|
   00000170  6d 6f 76 65 20 64 69 73  6b 73 20 6f 72 20 6f 74  |move disks or ot|
   00000180  68 65 72 20 6d 65 64 69  61 2e ff 0d 0a 44 69 73  |her media....Dis|
   00000190  6b 20 65 72 72 6f 72 ff  0d 0a 50 72 65 73 73 20  |k error...Press |
   000001a0  61 6e 79 20 6b 65 79 20  74 6f 20 72 65 73 74 61  |any key to resta|
   000001b0  72 74 0d 0a 00 00 00 00  00 00 00 00 00 00 ff ff  |rt..............|
   000001c0  ff ff ff ff ff ff ff ff  ff ff ff ff ff ff ff ff  |................|
   000001d0  ff ff ff ff ff ff ff ff  ff ff ff ff ff ff ff ff  |................|
   000001e0  ff ff ff ff ff ff ff ff  ff ff ff ff ff ff ff ff  |................|
   000001f0  ff ff ff ff ff ff ff ff  ff ff ff 6c 8b 98 55 aa  |...........l..U.|
   00000200
  • gdisk scan gives me: MBR:Protective, BSD: not present, APM: not present, GPT present – Marcin Pyszynski Jun 19 at 16:41
  • Buy a new, make a bit-for-bit copy and experiment with that – Thorbjørn Ravn Andersen Jun 19 at 19:03
  • @MarcinPyszynski: The only error message states the sector size is 0. The sector size is not stored in the GPT so the title of your question is confusing. Why do you think the problem is with the GPT? – David Anderson Jun 20 at 5:38
  • Can you post the output from the following command? sudo dd if=/dev/disk3s2 count=1 | hexdump -Cv. – David Anderson Jun 20 at 6:27
  • @DavidAnderson Hi David. I added output from this command to the body of main question. As I'm newbie (but very determined to learn something and repaired disk) my questions could be confusing... - sorry for that. Also when I try to see files (testdisk) on my disk3s2 partition it give me strange names with chinese symbols, and strange dates like 1906 ;-)... Also I noticed, that my other external disk (formated/partitioned about the same time) but working condition, has about the same configuration of partition - but the little partition is recognized (by diskutil) as a EFI. – Marcin Pyszynski Jun 20 at 11:16

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