Fix disk metric showing double the actual value (ray-project#32674) (r…

…ay-project#32993)

Signed-off-by: Alan Guo <aguo@anyscale.com>

the disks stats returns stats about two paths / and /tmp/ray. Since both those paths are on the same partition, disk_usage will return the same value. We do not need to combine them.

In the UI, we show the disk stats for / so I'll do the same for the metric as well.

dashboard/modules/reporter/reporter_agent.py

@@ -907,10 +907,8 @@ def _record_stats(self, stats, cluster_stats):
             value=disk_io_speed_stats[3],
             tags={"ip": ip},
         )
-        used, free = 0, 0
-        for entry in stats["disk"].values():
-            used += entry.used
-            free += entry.free
+        used = stats["disk"]["/"].used
+        free = stats["disk"]["/"].free
         disk_utilization = float(used / (used + free)) * 100
         disk_usage_record = Record(
             gauge=METRICS_GAUGES["node_disk_usage"], value=used, tags={"ip": ip}