howto/drbd.md

@@ -63,6 +63,37 @@ Finding which host is associated with this device is easy: just call
 
 It's the host `gettor-01`.
 
+## Deleting a stray device
+
+If Ganeti tried to create a device on one node but couldn't reach the
+other node (for example if the secondary IP on the other node wasn't
+set correctly), you will see this error in Ganeti:
+
+       - ERROR: node chi-node-03.torproject.org: unallocated drbd minor 0 is in use
+
+You can confirm this by looking at the `/proc/drbd` there:
+
+    root@chi-node-03:~# cat /proc/drbd 
+    version: 8.4.10 (api:1/proto:86-101)
+    srcversion: 473968AD625BA317874A57E 
+     0: cs:StandAlone ro:Secondary/Unknown ds:Inconsistent/DUnknown   r-----
+        ns:0 nr:0 dw:0 dr:0 al:8 bm:0 lo:0 pe:0 ua:0 ap:0 ep:1 wo:f oos:10485504
+
+And confirm the device does not exist on the other side:
+
+    root@chi-node-04:~# cat /proc/drbd 
+    version: 8.4.10 (api:1/proto:86-101)
+    srcversion: 473968AD625BA317874A57E
+
+The device can therefore be deleted on the `chi-node-03` side. First
+detach it:
+
+    drbdsetup detach /dev/drbd0
+
+Then delete it:
+
+    drbdsetup del-minor 0
+
 ## Pager playbook
 
 ### Resyncing disks