Description of problem:
After draining nodes both pods (prometheus-k8s-0 and prometheus-k8s-1) restarted and all data that was previously collected by metrics removed from a cluster

Version-Release number of selected component (if applicable):
CNV-4.10

How reproducible:
100%

Steps to Reproduce:
1. drain first node where pod prometheus-k8s-0 is running
2. return node back and drain second node where prometheus-k8s-1 is running
3. check metrics on a cluster - old data removed

Actual results:
Metrics cleared when both pods prometheus-k8s-0 and prometheus-k8s-1 restarted

Expected results:
Old data should be kept

Additional info:
I guess some persistent storage should be using for keeping all metrics:
https://docs.openshift.com/container-platform/4.9/monitoring/configuring-the-monitoring-stack.html#configuring-persistent-storage