Primary download mirrors和Secondary download mirrors区别

官网下载页面最下面这样说
Note: Primary download mirrors are synchronized with Linux Mint on a daily basis. Secondary mirrors either don't synchronize as often, or only synchronize part of of the entire public Linux Mint archive.
亦即：primary镜像源每天同步，secondary镜像源跟主服务器同步没有这么高的频率，或者只同步一部分文件。其实secondary里面的中科大的源不错的，尤其是对教育网用户