the zstor -c <zstor_config.toml> status command gives an overview of the backend 0-db's, if they are reachable or not and the storage space they consume.
0-stor collects metrics about the system. It can be configured with a 0-db-fs mountpoint, which will trigger 0-stor to collect 0-db-fs statistics, next to some 0-db statistics which are always collected. If the prometheus_port config option is set, 0-stor will serve metrics on this port for scraping by prometheus.
They are available over http on the configured port at the /metrics path.
Test it with curl localhost:9100/metrics for example.
If a 0-db backend is broken (the host is down for example) it needs to be replaced.
Replace the malfunctioning 0-db's with new ones in the zstor config.
For zstor to reload the config, send it a SIGUSR1 signal (kill -SIGUSR1) or restart the entire qsfs system.
The 0-stor repair subsystem will take care of rebulding the data, regenerating the shards, and storing the new shards on the new 0-db's.