I have a serious problem with my TimeMachine external 8TB Seagate.
It has been used as my TimeMachine disk. Did a full backup, installed lastest OS X from scratch and the external disk will no longer mount.
My pictures are on this disk. Here are the commands I have run to try and fix this.
I don't want to use DiskWarrior or any other Thirdparty software.

    diskutil list
    /dev/disk0 (internal, physical):
       #:                       TYPE NAME                    SIZE       IDENTIFIER
       0:      GUID_partition_scheme                        *250.1 GB   disk0
       1:                        EFI EFI                     209.7 MB   disk0s1
       2:                 Apple_APFS Container disk1         124.7 GB   disk0s2
       3:       Microsoft Basic Data DEBIAN                  124.5 GB   disk0s3
       4:                 Apple_Boot Recovery HD             650.0 MB   disk0s4
    
    /dev/disk1 (synthesized):
       #:                       TYPE NAME                    SIZE       IDENTIFIER
       0:      APFS Container Scheme -                      +124.7 GB   disk1
                                     Physical Store disk0s2
       1:                APFS Volume OSX                     21.4 GB    disk1s1
       2:                APFS Volume Preboot                 22.9 MB    disk1s2
       3:                APFS Volume Recovery                512.0 MB   disk1s3
       4:                APFS Volume VM                      20.5 KB    disk1s4
    
    /dev/disk2 (external, physical):
       #:                       TYPE NAME                    SIZE       IDENTIFIER
       0:      GUID_partition_scheme                        *8.0 TB     disk2
       1:                        EFI EFI                     209.7 MB   disk2s1
       2:          Apple_CoreStorage Seagate                 8.0 TB     disk2s2
       3:                 Apple_Boot Boot OS X               134.2 MB   disk2s3
    
    /dev/disk3 (external, virtual):
       #:                       TYPE NAME                    SIZE       IDENTIFIER
       0:                  Apple_HFS Seagate                +8.0 TB     disk3
                                     Logical Volume on disk2s2
                                     784988D6-B233-4BFC-AB1C-45EA7FF24640
                                     Unencrypted
    
    sudo fsck_hfs -l /dev/disk3
    
    ** /dev/rdisk3 (NO WRITE)
       Executing fsck_hfs (version hfs-407.50.6).
    ** Performing live verification.
    ** Checking Journaled HFS Plus volume.
       The volume name is Seagate
    ** Checking extents overflow file.
       Invalid leaf record count
       (It should be 190 instead of 192)
    ** Checking catalog file.
       Invalid sibling link
    (4, 318227)
    ** The volume Seagate was found corrupt and needs to be repaired.
    
    sudo fsck_hfs -r
    
    ** /dev/rdisk3
       Executing fsck_hfs (version hfs-407.50.6).
    ** Checking Journaled HFS Plus volume.
       The volume name is Seagate
    ** Checking extents overflow file.
       Invalid leaf record count
       (It should be 190 instead of 192)
    ** Checking catalog file.
    ** Rebuilding catalog B-tree.
    ** The volume Seagate could not be repaired.