Share /usr/portage via NFS
Recently I have tried sharing /usr/portage among several boxes via NFS after I've read http://www.gentoo.org/proj/en/portage/doc/faq.xml.
I followed portage's manpage, created /etc/portage/modules on nfs client
$ cat /etc/portage/modules
portdbapi.auxdbmodule = cache.metadata_overlay.database
And removed all cache files under /var/cache/edb/dep/usr/portage
So that I don't need to run emerge --metadata on nfs client after emerge --sync.
It is not over yet for eix users. If you have a $HOME/.eixrc and defines in it PORTDIR_CACHE_METHOD as something like "portage-2.1"/"cdb"/"sqlite"(check man eix), you may want to remove the ~/.eixrc file. Since those methods requires you to run emerge --metadata before update-eix, and thus defeat our purpose in the first place.