Best app to compare two hard drives?

[AVR2]

I'm looking for an app that can compare external hard drive A to external hard drive B (which is currently a partial backup of A) and then copy files from A to B as necessary to make B a full backup of A. Any recommendations?

 

[kohlson]

Carbon Copy Cloner or Super Duper.

 

[BrianBaughn]

OP: Is the folder heirarchy the same for the original A as it is on the backup B?

 

[HDFan]

Both programs do disk cloning, so yes, unless you select only specific folders to copy.