lftp -e 'open http://<some.site>/centos/ && mirror -c --delete 7 && exit'

lftp -e 'open http://mirror.eu.oneandone.net/linux/distributions/centos/ && mirror -c --delete 7/fasttrack && mirror -c --delete 7/extras && mirror -c --delete 7/updates && exit'

Quellen

http://wiki.centos.org/HowTos/CreateLocalMirror