Now that the master CPAN repository is hosted by Perl NOC, the first ring of mirrors can use a new “fast sync” rsync that allows any mirror to get updates within 30 seconds of a file changing in the main repository. To use this new fast sync, you need a username/password to connect to the rsync server on the master server. Send mail to email@example.com to request credentials. Anyone mirroring from FUnet directly should make the switch.
The NOC crew detailed instructions for instant mirroring on the Github wiki.