TrueNAS Scale Pool Metrics
TrueNAS Core, the BSD based version of TrueNAS, includes metrics outputs that come with pool usage statistics, something you may expect from a storage operating system. TrueNAS Scale, the Linux base version includes many performance metrics that you can export, but surprisingly not pool usage.
For my home metrics, I use Prometheus, InfluxDB, and Grafana. To solve the lack of pool usage metrics, I started considering the project https://github.com/bdinpoon/upsmonitor which I use to take UPS metrics and report them to InfluxDB.
This led me to the following steps to collect TrueNAS pool metrics, through InfluxDB and Grafana. I hope it helps you too!