Problem with disk repair I have HDD connected to my Mac which is formatted with HFS and I use for backups.
I have noticed a problem while running fdisk and fsck_hfs:
sudo fsck_hfs -rd /dev/disk1s1
Password:
journal_replay(/dev/disk1s1) returned 0
** /dev/rdisk1s1
    Using cacheBlockSize=32K cacheTotalBlock=65536 cacheSize=2097152K.
   Executing fsck_hfs (version hfs-522.100.5).
** Checking Journaled HFS Plus volume.
   The volume name is Backup
** Checking extents overflow file.
** Checking catalog file.
** Rebuilding catalog B-tree.
BlockFindAll:  found 1489232 blocks but needed 1572864
   Disk full error
** The volume Backup could not be repaired.
    volume type is pure HFS+ 
    primary MDB is at block 0 0x00 
    alternate MDB is at block 0 0x00 
    primary VHB is at block 2 0x02 
    alternate VHB is at block 1953521662 0x74705ffe 
    sector size = 512 0x200 
    VolumeObject flags = 0x07 
    total sectors for volume = 1953521664 0x74706000 
    total sectors for embedded volume = 0 0x00 
    CheckHFS returned 8, fsmodified = 0

The disk is not full.
Is there anything I can which does not involve reformatting or buying a new disk?
It's a WD Red 1TB about 5 years old. Perhaps it's time to buy a new one after all?
Thanks
Honestly the best bet is to copy the files on that disk elsewhere, reformat your disk and then copy the stuff back. That would be your cheapest and safest procedure.
The next thing to do would be a third party disk repair tool. I use DiskWarrior and as it is an HFS disk it will work fine (DW doesn't work on APFS disks) There is also TechTool Pro, Drive Genius and others. But I have no specific experience with those.