It can be hard to mirror CPAN because CPAN is big :
500,000+ objects.
CPAN offers a solution : with instant mirroring you can
track the changes in CPAN.
iim does instant mirroring ; it picks up the changes
in CPAN, and applies them to your mirror.
iim starts mirroring right after start-up ;
if the local copy is too much out-of-date, a full rsync is done first ;
then, iim starts tracking the changes in the CPAN master archive.