diff --git a/fuel_tests/tests/test_discovery_slave.py b/fuel_tests/tests/test_discovery_slave.py
index 7b1670089..8d7e969e8 100644
--- a/fuel_tests/tests/test_discovery_slave.py
+++ b/fuel_tests/tests/test_discovery_slave.py
@@ -148,7 +148,7 @@ class TestNodeDiskSizes(object):
         self.manager.show_step(7)
         fuel_web.verify_network(cluster_id)
 
-        self.manager.show_step(6)
+        self.manager.show_step(8)
         fuel_web.run_ostf(
             cluster_id=cluster_id,
             test_sets=['ha', 'smoke', 'sanity'])
diff --git a/fuelweb_test/models/fuel_web_client.py b/fuelweb_test/models/fuel_web_client.py
index 2a6239583..be6c75e8e 100644
--- a/fuelweb_test/models/fuel_web_client.py
+++ b/fuelweb_test/models/fuel_web_client.py
@@ -1119,7 +1119,8 @@ class FuelWebClient29(object):
     def get_cluster_block_devices(self, node_name):
         logger.info('Get %s node block devices (lsblk)', node_name)
         with self.get_ssh_for_node(node_name) as remote:
-            return remote.check_call('/bin/lsblk').stdout_str
+            # Note: 'lsblk' comand returns some undecodable symbols
+            return ''.join(remote.check_call('/bin/lsblk')['stdout'])
 
     @logwrap
     def get_pacemaker_status(self, controller_node_name):