Got an old Samsung 640 GB external HD I used for encrypted Time Machine
backups several years ago. I tried looking at it today and it was error
message city.

It won't mount and failed the Disk Utility First Aid scan. Any ideas way
to get at the (not really important) data?

Text of 3 ERROR MESSAGES FROM DISK UTILITY runs follow:
1.
Could not mount “Samsung 640”. (com.apple.DiskManagement.disenter error
49217.)

2.
Running First Aid on “Samsung 640” (disk5s1)

Checking file system and repairing if necessary and if possible.
Volume is already unmounted.
Performing fsck_apfs -y -x /dev/rdisk5s1
Checking the container superblock.
error: (oid 0xf5398) om: invalid o_oid (0x403)
error: (oid 0xf5398) om: invalid o_type (0xd, expected 0x4000000b)
error: (oid 0xf5398) om: invalid o_type (0xd, expected 0x4000000b)
error: verification/reading of the omap object failed: Illegal byte sequence
warning: checkpoint 243 (xid 67042) failed consistency check
error: (oid 0xf574c) om: bt: invalid o_type (0x40000018, expected
0x40000002)
error: (oid 0xf574c) om: bt: invalid o_subtype (0x0, expected 0xb)
warning: checkpoint 241 (xid 67041) failed consistency check
error: (oid 0xf5a66) om: invalid o_type (0x40000002, expected 0x4000000b)
error: verification/reading of the omap object failed: Illegal byte sequence
warning: checkpoint 239 (xid 67040) failed consistency check
Checking the checkpoint with transaction ID 67039.
warning: container has been mounted by APFS version 1934.141.2, which is
newer than 1934.121.2
warning: disabling overallocation repairs by default; use -o to override
Checking the EFI jumpstart record.
Checking the space manager.
Checking the space manager free queue trees.
Checking the object map.
Checking the encryption key structures.
Checking volume /dev/rdisk5s1.
Checking the APFS volume superblock.
The volume Samsung 640 was formatted by hfs_convert (945.275.7) and last
modified by apfs_kext (1933.61.1).
Checking the object map.
error: (oid 0xf5080) gbitmap: invalid o_type (0x4000001c, expected
0x40000019)
error: could not retrieve gbitmap from er_state_phys_t
Encryption Rolling data structures are invalid.
The volume /dev/rdisk5s1 was found to be corrupt and cannot be repaired.
Verifying allocated space.
The volume /dev/rdisk5s1 could not be verified completely.
File system check exit code is 8.
Restoring the original state found as unmounted.
File system verify or repair failed. : (-69845)

Operation failed…

3.
Volume name : Samsung 640
Volume type : APFS Volume
BSD device node : disk5s1
File system : APFS (Encrypted)
Connection : USB
Device tree path :
IODeviceTree:/arm-io@10F00000/usb-drd1@2280000/usb-drd1-port-hs@01100000
Writable : No
Is case-sensitive : No
File system UUID : 79213D85-0DCA-39F2-A27E-37D421C72059
Volume capacity : 639,686,197,248
Owners enabled : No
Is encrypted : Yes
Can be verified : Yes
Can be repaired : Yes
Bootable : No
Journaled : No
Disk number : 5
Partition number : 1
Media name :
Media type : Generic
Ejectable : Yes
Solid state : No
S.M.A.R.T. status : Not Supported
Parent disks : disk5

On 07/08/2022 23:28, Wade Garrett wrote:
> Got an old Samsung 640 GB external HD I used for encrypted Time Machine
> backups several years ago. I tried looking at it today and it was error
> message city.
>
> It won't mount and failed the Disk Utility First Aid scan. Any ideas way
> to get at the (not really important) data?
>
<SNIP>

You could try Disk Drill

https://www.cleverfiles.com

It has worked for me, even on a damaged Microsoft Windows machine!

--
Kind regards,
David B.