howto/drbd.md

@@ -67,6 +67,17 @@ secondary with:
 
     gnt-instance replace-disks -n fsn-node-03 gettor-01
 
+## Finding device associated with traffic
+
+If there's a lot of I/O (either disk or network) on a host and you're
+looking for the device (and therefore virtual machine, see above)
+associated with it, look in the [DRBD dashboard](https://grafana.torproject.org/d/e89a8da5-753f-4ee5-a1f3-93616c9246d6/drbd), in the "Disk I/O
+device details" row, which will show the exact device associated with
+the I/O.
+
+Then you can use the device number to find the associated virtual
+machine, see above.
+
 ## Deleting a stray device
 
 If Ganeti tried to create a device on one node but couldn't reach the