After a series of problems with my Mac Pro (2008), I was forced to take my machine in to the local Apple store, where they re-installed the operating system. This helped, but did not solve all the problems. I found the machine was running very slowly, and there seemed to be a lot more disk activity than I was aware of. I had previously used the Disk Utility (it saw problems but could not fix them), and TechTool Deluxe (it made changes, but didn't solve the problems), I finally purchased DiskWarrior.

DiskWarrior was able to re-build the file system, and since using it my machine has been back to its original high levels of performance.

I don't know how it works, but in my experience, DiskWarrior was able to fix problems that other utilities could not. For that reason it receives my highest recommendation.