What are recommended threshold for Linux performance metrics?
I'm collecting statistics from remote servers using rstatd.
On which values should I issue warnings? errors?
establish baseline under normal load and start from there. that's it.
As pQd already mentioned, it's best to know what's the baseline, intervene when the state deviates from there.
As for specific thresholds that shouldn't be exceeded if you want the server to be snappy:
Though it all depends on the kind of workloads you're running. For example, you can have higher load avg if you have many low priority (with high niceness) jobs in the background.