To collectd metrics from servers I use databases/opentsdb and net-mgmt/collectd5.

UPDATE

This patch has been merged with this

Collectd5 can natively use an OpenTSDB database as output but when you use the FreeBSD port, this output plugin isn't included (don't ask me why): here is how to patch net-mgmt/collectd5 to include it.

Basically we need to apply to Makefile this patch:

--- Makefile.orig       2016-04-04 07:04:56.231162000 -0400
+++ Makefile    2016-04-04 06:58:51.146676000 -0400
@@ -24,7 +24,8 @@

 OPTIONS_DEFINE=                CGI DEBUG GCRYPT LOGSTASH VIRT
 OPTIONS_GROUP=         INPUT OUTPUT
-OPTIONS_GROUP_OUTPUT=  KAFKA MONGODB NOTIFYDESKTOP NOTIFYEMAIL RIEMANN RRDTOOL
+OPTIONS_GROUP_OUTPUT=  KAFKA MONGODB NOTIFYDESKTOP NOTIFYEMAIL RIEMANN RRDTOOL \
+                       TSDB
 OPTIONS_GROUP_INPUT=   CURL CURL_JSON CURL_XML DBI IPMI JSON MEMCACHEC \
                        MODBUS MYSQL NUTUPS OLSRD ONEWIRE OPENLDAP \
                        PERL PGSQL PINBA PING PYTHON RABBITMQ REDIS ROUTEROS \
@@ -67,6 +68,7 @@
 STATGRAB_DESC=         Enable statgrab-based plugins (interface, etc)
 STATSD_DESC=           Enable statsd plugin
 TOKYOTYRANT_DESC=      Enable tokyotyrant plugin
+TSDB_DESC=             Enable write_tsdb plugin
 VARNISH_DESC=          Enable varnish 4.x cache statistics
 VIRT_DESC=             Enable libvirt plugin (requires XML)
 XML_DESC=              Enable XML plugins
@@ -247,6 +249,8 @@
 TOKYOTYRANT_CONFIGURE_ENABLE=  tokyotyrant
 TOKYOTYRANT_CONFIGURE_WITH=    libtokyotyrant=${LOCALBASE}

+TSDB_CONFIGURE_ENABLE=         write_tsdb
+
 VARNISH_LIB_DEPENDS=           libvarnishapi.so:${PORTSDIR}/www/varnish4
 VARNISH_CONFIGURE_ENABLE=      varnish
 VARNISH_CONFIGURE_WITH=                libvarnish=${LOCALBASE}

and this to pkg-plist:

--- pkg-plist.orig      2016-04-04 07:04:41.492617000 -0400
+++ pkg-plist   2016-04-04 07:04:26.272999000 -0400
@@ -72,6 +72,7 @@
 %%SIGROK%%lib/collectd/sigrok.so
 %%SNMP%%lib/collectd/snmp.so
 %%STATSD%%lib/collectd/statsd.so
+%%TSDB%%lib/collectd/write_tsdb.so
 lib/collectd/swap.so
 lib/collectd/syslog.so
 lib/collectd/table.so

That's all, folks!