Mirrors are servers where you download the data for your installation or update. You have to
select mirrors near you during the installation and you might want to change them in the future. The
last line of /etc/make.conf
contains URL’s to the download mirrors.
Emerge looks one after another. You can modify this line to get your preferred mirrors in front, or you
can delete the not wanted.
GENTOO_MIRRORS="ftp://mirror.switch.ch/mirror/gentoo/ http://ftp.easynet.nl/mirror/gentoo/ ftp://gentoo.llarian.net/pub/gentoo"
This can also be completely missing, sometimes even better, since mirrors might not be synchronized.
The following list (or similar) can also be put in
/etc/make.conf
to use a rsync server, to increase speed of updating
the portage tree.
SYNC="rsync://rsync.de.gentoo.org/gentoo-portage"
However this seems to be outdated, since emerge checks on its own initiative whether or not a rsync sever is present.
In fact there are different ways how to get the portage tree updated from the mirrors: emerge --sync that uses rsync protocol and might run into problems with firewalls
emerge–webrsync that gets a daily snapshot from a mirror, than this local copy will be used to synchronize the portage what obviously is the approach that is more time consuming.
emerge–delta-webrsync that is similar as emerge–webrsync downloads just the difference between the local snapshot and the snapshot on the Mirror. However first this package must be installed emerge emerge–delta-webrsync