Mac disk utility updating boot support partitions
You could try another disk repair utility (disk Warrior, techtool, etc...), or if you have a recent backup I would be tempted to wipe the drive and start over.
If you have another Mac you could put that Mac into target disk mode, connect the two via Firewire or Thunderbolt and try the repair that way.
With the below mentioned partition managers you can easily execute disk level partitioning on an internal and external hard drive.
The problem here is that disk utility is usually not smart enough to know when to give up.
You can just format the selected operating system partition only.2.
Increased Data Security: There is an increased security of files and folder stored on the partition since the data is now also available on the other partition of the Windows/Mac OS hard drive.
Top 4 Partition Manager Software for Windows and Mac OS:1.
Stellar Partition Manager Software The Mac hard drives partition manager tool helps the user to create, resize the partition on their Macintosh HDs.