port drbd pager playbook to prometheus

howto/drbd.md

@@ -114,14 +114,13 @@ Then that device map can be removed with:
 
 ### Resyncing disks
 
-In Nagios, if you see this warning:
+A `DRBDDegraded` alert looks like this:
 
-    DRBD CRITICAL: Device 10 WFConnection UpToDate, Device 9 WFConnection UpToDate
+    DRBD has 1 out of date disks on fsn-node-04.torproject.org
 
-It means that, on that host (in my case it was
+It means that, on that host (in this case
 `fsn-node-04.torproject.org`), disks are desynchronized for some
-reason. In this case, those are disks 9 and 10. You can confirm that
-on the host:
+reason. You can confirm that on the host:
 
     # ssh fsn-node-04.torproject.org cat /proc/drbd
     [...]
@@ -132,7 +131,8 @@ on the host:
     [...]
 
 You need to find which instance this disk is associated with (see also
-above):
+above), by asking the Ganeti master for the DRBD disk listing with
+`gnt-node list-drbd $NODE`:
 
     $ ssh fsn-node-01.torproject.org gnt-node list-drbd fsn-node-04
     [...]