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I have an external hard drive that has two partitions and one of them is not being mounted. The one that is not being mounted has data I would like to recover. Right before the problem I had installed OS X Mojave on it but after once booting into it, on a reboot I just got a blank screen. So I restarted the mac and discovered that the partition itself cannot be mounted.

I have gone through a fair bit of article on this forum and elsewhere on this and I am going to give the information I think may be relevant. The disk in question is /dev/disk2

The output of diskutil list is:

/dev/disk0 (internal, physical):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *251.0 GB   disk0
   1:                        EFI EFI                     209.7 MB   disk0s1
   2:          Apple_CoreStorage Macintosh HD            250.1 GB   disk0s2
   3:                 Apple_Boot Recovery HD             650.0 MB   disk0s3
/dev/disk1 (internal, virtual):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:                  Apple_HFS Macintosh HD           +249.8 GB   disk1
                                 Logical Volume on disk0s2
                                 21851A15-0785-48A0-A736-0FEF2E06952B
                                 Unencrypted
/dev/disk2 (external, physical):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *1.0 TB     disk2
   1:                        EFI EFI                     209.7 MB   disk2s1
   2:                  Apple_HFS Untitled 1              300.0 GB   disk2s2
   3: 7C3457EF-0000-11AA-AA11-00306543ECAC               699.8 GB   disk2s3

The output of sudo gpt -r show disk2 is

       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   585937504      2  GPT part - 48465300-0000-11AA-AA11-00306543ECAC
   586347144      262144         
   586609288  1366848848      3  GPT part - 7C3457EF-0000-11AA-AA11-00306543ECAC
  1953458136           7         
  1953458143          32         Sec GPT table
  1953458175           1         Sec GPT header

The output of sudo hexdump -Cv -n 512 /dev/disk2s3 is

00000000  c0 eb e0 54 ab 54 c5 33  01 00 00 00 00 00 00 00  |...T.T.3........|
00000010  ca 02 00 00 00 00 00 00  01 00 00 80 00 00 00 00  |................|
00000020  4e 58 53 42 00 10 00 00  aa 0e 2f 0a 00 00 00 00  |NXSB....../.....|
00000030  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
00000040  02 00 00 00 00 00 00 00  05 69 77 e5 1b 75 49 0e  |.........iw..uI.|
00000050  81 7c 14 7b c7 2c e5 35  a5 e2 00 00 00 00 00 00  |.|.{.,.5........|
00000060  cb 02 00 00 00 00 00 00  18 01 00 00 44 6c 00 00  |............Dl..|
00000070  6d 3a 09 00 00 00 00 00  8e 90 08 00 00 00 00 00  |m:..............|
00000080  21 00 00 00 01 38 00 00  1f 00 00 00 02 00 00 00  |!....8..........|
00000090  da 37 00 00 27 00 00 00  39 3e 00 00 00 00 00 00  |.7..'...9>......|
000000a0  05 30 10 00 00 00 00 00  01 04 00 00 00 00 00 00  |.0..............|
000000b0  00 00 00 00 64 00 00 00  03 04 00 00 00 00 00 00  |....d...........|
000000c0  06 04 00 00 00 00 00 00  31 3e 00 00 00 00 00 00  |........1>......|
000000d0  2c dd 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |,...............|
000000e0  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
000000f0  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
00000100  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
00000110  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
00000120  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
00000130  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
00000140  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
00000150  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
00000160  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
00000170  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
00000180  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
00000190  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
000001a0  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
000001b0  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
000001c0  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
000001d0  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
000001e0  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
000001f0  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
00000200

I was largely following what sounded to be a similar problem but in my case I find that the container is APFS. So that didn't help.

Furthermore, I tried TestDisk based on but it gave me the wrong starting and ending sectors (which I realized among other ways by hexdump).

To be honest, at this point I do not even see how to see there is a problem from the diagnostics above except that disk2s3 does not mount.

One more point, I looked at the disk through Steller Data Recovery Professional and find the files I am interested in. However, (a) I do not want to pay the price of an external hard drive for a one time recovery and (b) I want to understand what is going on and it feels like there should be a simple fix to this problem.

EDIT: Based on Tetsujin's comment I realized something funny. I have OSX 10.11.6 so indeed it should not be able to read an APFS formatted disk. What I do not understand is how my disk2s3 became APFS. Is it because I installed Mojave on it? Is there a way to make it go back to whatever it was (I do not know what it was). Can I use gdisk to try HFS/HFS+ without destroying the data? The reason I think something else is wrong is because I was not able to boot from the disk either.

  • What OS are you currently booted to? Something that knows what APFS is? – Tetsujin Jan 18 at 9:50
  • I am on OS X 10.11.6 and was on this earlier too when the disk2s3 was being mounted. Any excursions outside of this were when I installed Mojave on the same disk2s3 and booted from it. – FrenchMacUser Jan 18 at 9:53
  • @Tetsujin That was a very good question. I hadn't done my homework and had not realized that APFS is not readable by OSX 10.11.6. I have made an edit to my question. – FrenchMacUser Jan 18 at 10:19
  • What is the model/year of your Mac ? – David Anderson Jan 18 at 12:08
  • MacBook Pro (Retina, 13-inch, Early 2015) – FrenchMacUser Jan 18 at 17:06

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