Commands from https://docs.librenms.org/Extensions/RRDCached/

Create System Service

sudo vi /etc/systemd/system/rrdcached.service

[Unit]
 Description=Data caching daemon for rrdtool
 After=network.service
 [Service]
 Type=forking
 PIDFile=/run/rrdcached.pid
 ExecStart=/usr/bin/rrdcached -w 1800 -z 1800 -f 3600 -s librenms -U librenms -G librenms -B -R -j /var/tmp -l unix:/run/rrdcached.sock -t 4 -F -b /opt/librenms/rrd/
 [Install]
 WantedBy=default.target

Save with esc + :wq

Enable rrdcached service on boot up and start the service now

systemctl enable --now rrdcached.service

Enable RRDcached in librenms config

vi /opt/librenms/config.php

add/edit the following line. If it is commented out, uncomment it

$config['rrdcached'] = "unix:/run/rrdcached.sock";

Save with esc + :wq

Check the disk IO after a little bit to see if it went down.