Fixed error

docs/metrics.md

@@ -141,6 +141,12 @@ Enabled with `metrics.sdn`. Labels are `cluster`, `node`, `sdn`, and `sdn_id`.
 | --- | --- |
 | `pve_sdn_state` | `1` when the SDN resource status is `ok`, otherwise `0`. |
 
+PVE 8 reports SDN zones as `sdn` cluster resources, PVE 9 reports them as
+`network` resources (zones and fabrics). Both are exported as `pve_sdn_state`;
+the `sdn` label holds the zone or fabric name and `sdn_id` the resource ID,
+which differs between the two formats (`sdn/<node>/<zone>` versus
+`network/<node>/<network-type>/<name>`).
+
 ## LXC containers
 
 Enabled with `metrics.lxc`. Templates are skipped. Labels are `cluster`,