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.