Save logs with loki

I would like to save my logs from multiple servers in one. That’s why I use one Promtail instance for each server and I send logs only to one Loki instance.
I have a basic configuration for Loki with no saving period. I want to save my logs in the local server for 6 months. Is that possible? If yes can you help me configuring it?

Also, is there a problem that I have only one instance for Loki (because I have multiple Promtail instances) ?

Thank you!