In my observation, Linux distributions take the largest disk space in our ftp mirror site. But the network connection speed between Taiwan and US is vary slow (usually only 3Mbit). When a linux distribution announced a new release version, we have to spent almost one week to sync with US mirror site. This decrease our service quality and available of FTP site.
I know that many Linux distributions in order to offer online-installation (installation via FTP or HTTP site), almost all of the files in ISO Images and FTP site are the same. Therefore, we can manual fetch ISO Images from neighbor country, for example, Japan, and mount these ISO Image to copy files to appropriate location in FTP site. Then use rsync to sync with US mirror site and check if all files have mirrored completely. This idea can reduce data transmission time and make ftp server offer new release version quicky.