[Bug-tar] help with incremental backups

[Nick]

I apologize if there is readily available information that I have overlooked.

I would like to do incremental backups using GNU tar but the namespace 
operations are very slow on my filesystem and GNU tar traverses the entire
directory structure before dumping any data. In some cases, this
can take up to 24 hours! 

I would like to modify GNU tar so that it does not perform a traversal but I
am unclear as to why the traversal is necessary for incremental backups
in particular. Could someone fill me in or point me to some documentation?

Thanks very much.

Nick