Open APM Data Source / Collectors

We are currently using graphite and influxDB together with telegraf to collect data which we then display with Grafana.
We are having issues with scalability and redundancy, and the InfluxDB HA solution isn’t free, so that’s not an option.

We were wondering if we can get some suggestions for backend data storage solutions which support innate HA, are free, and can work with data collectors such as Telegraf or any other.

We use telegraf on Windows and Linux servers to collect performance data and run scripts. If there is a different collector which we can replace telegraf with an gain an HA database/storage backend platform that would be acceptable.

Of course, the entire solution must work and be supported by Grafana!