Can I speed up Disk Utility First Aid by running “fsck_hfs” with the “-c” option?
There are some sources saying you should set the cache size to maybe 1/2 of your installed memory.
This source says, that fsck_hfs is running a lot faster if you assign it 2200m cache (in this example for a 1TB drive):
http://hints.macworld.com/article.php?story=20110829063745320
I'm now going to experiment with that setting because my external 6TB time machine backup disk has fsck_hfs running since about 18 hours.