What does remote read means in Prometheus?

Question

We would like to use VictoriaMetric as storage DB for time-series data that is collected from Prometheus. But it's said in the doc that this integration is only supported in write mode and not the read one.

1. Does it mean that prometheus will only be used as a collector of time-series data and the PromQL to read that data won't be available?
2. Does Prometheus will stop to store collected data in filesystem and only use remote storage if we specify remote write configuration? Or the collected data will still be available from the filesystem and we can collect real-time data from Prometheus and if we need historic long-term data we have to query the DB itself?

Answer 1

Does it mean that prometheus will only be used as a collector of time-series data and the PromQL to read that data won't be available?

VictoriaMetrics supports PromQL and Prometheus querying API, so it can be used as drop-in replacement for Prometheus when querying via Grafana. See these docs for more details.

Single-node VictoriaMetrics may scrape targets that expose metrics in Prometheus text exposition format - see these docs for details.

Does Prometheus will stop to store collected data in filesystem and only use remote storage if we specify remote write configuration? Or the collected data will still be available from the filesystem and we can collect real-time data from Prometheus and if we need historic long-term data we have to query the DB itself?

Prometheus continues storing the collected data in local storage according to the configured retention while replicating the data to remote storage. So both the original Prometheus and remote storage can be queried at any time.