k3s, by default, uses sqlite for storage instead of etcd. This is one of the ways you can get a performance improvement.

If you are going to run a cluster you're likely going to want to have your database be an HA cluster. While k3s can support other databases, like PostgreSQL, it doesn't have handling for clusters in the config.

This is a limitation I see for k3s in clusters, right now.

I would love to see cluster handling in k3s. etcd can be a scaling bottleneck and replacing it with PostgreSQL could help it scale much higher.

Disclaimer, I work on Rancher Desktop which uses k3s