fence_sbd do not shutdown node in fencing operation

hi

i have configure the stonith on my cluster (two node redhat server enterprise 7.4) with fence_sbd
i have setted stonith-action property to "off".
When i excute the fencing command for a node, it reboots instead of shutdown

output command pcs status:

[root@nodo1-cluster-res7x64 ~]# pcs status
Cluster name: testcluster1
Stack: corosync
Current DC: nodo1-cluster-res7x64 (version 1.1.16-12.el7_4.2-94ff4df) - partition with quorum
Last updated: Mon Oct 2 15:26:38 2017
Last change: Mon Oct 2 12:52:12 2017 by root via cibadmin on nodo1-cluster-res7x64

2 nodes configured
5 resources configured

Online: [ nodo1-cluster-res7x64 nodo2-cluster-res7x64 ]

Full list of resources:

Resource Group: apachegroup
my_lvm (ocf::heartbeat:LVM): Started nodo2-cluster-res7x64
filesystem_cluster (ocf::heartbeat:Filesystem): Started nodo2-cluster-res7x64
VirtualIP (ocf::heartbeat:IPaddr2): Started nodo2-cluster-res7x64
Website (ocf::heartbeat:apache): Started nodo2-cluster-res7x64
Stonit_SBD (stonith:fence_sbd): Started nodo1-cluster-res7x64

Daemon Status:
corosync: active/enabled
pacemaker: active/enabled
pcsd: active/enabled
sbd: active/enabled

output command pcs property:

[root@nodo1-cluster-res7x64 ~]# pcs property
Cluster Properties:
cluster-infrastructure: corosync
cluster-name: testcluster1
dc-version: 1.1.16-12.el7_4.2-94ff4df
have-watchdog: true
last-lrm-refresh: 1506700393
stonith-action: off
stonith-enabled: true
stonith-watchdog-timeout: 0
[root@nodo1-cluster-res7x64 ~]#

Carlo