diff --git a/actions.yaml b/actions.yaml
index 2d2f1729..84259dbd 100644
--- a/actions.yaml
+++ b/actions.yaml
@@ -230,6 +230,12 @@ crushmap-update:
   additionalProperties: false
 show-disk-free:
   description: Show disk utilization by host and OSD.
+  params:
+    format:
+      type: string
+      enum: [json, json-pretty, xml, xml-pretty, plain]
+      default: "plain"
+      description: Output format, either json, json-pretty, xml, xml-pretty, plain; defaults to plain
   additionalProperties: false
 set-noout:
   description: Set ceph noout across the cluster.
diff --git a/actions/show-disk-free.py b/actions/show-disk-free.py
index 2ba7894f..1f38f094 100755
--- a/actions/show-disk-free.py
+++ b/actions/show-disk-free.py
@@ -18,12 +18,14 @@ import sys
 
 sys.path.append('hooks')
 from subprocess import check_output, CalledProcessError
-from charmhelpers.core.hookenv import log, action_set, action_fail
+from charmhelpers.core.hookenv import log, action_get, action_set, action_fail
 
 if __name__ == '__main__':
+    # constrained to enum: json,json-pretty,xml,xml-pretty,plain
+    fmt = action_get("format")
     try:
         out = check_output(['ceph', '--id', 'admin',
-                            'osd', 'df', 'tree']).decode('UTF-8')
+                            'osd', 'df', 'tree', '-f', fmt]).decode('UTF-8')
         action_set({'message': out})
     except CalledProcessError as e:
         log(e)
diff --git a/tests/basic_deployment.py b/tests/basic_deployment.py
index 2aeaa2a8..a15d7b01 100644
--- a/tests/basic_deployment.py
+++ b/tests/basic_deployment.py
@@ -17,6 +17,7 @@
 import amulet
 import re
 import time
+import json
 
 from charmhelpers.contrib.openstack.amulet.deployment import (
     OpenStackAmuletDeployment
@@ -117,7 +118,7 @@ class CephBasicDeployment(OpenStackAmuletDeployment):
         # Include a non-existent device as osd-devices is a whitelist,
         # and this will catch cases where proposals attempt to change that.
         ceph_osd_config = {
-            'osd-reformat': 'yes',
+            'osd-reformat': True,
             'ephemeral-unmount': '/mnt',
             'osd-devices': '/dev/vdb /srv/ceph /dev/test-non-existent'
         }
@@ -716,6 +717,27 @@ class CephBasicDeployment(OpenStackAmuletDeployment):
         action_id = u.run_action(sentry_unit, 'get-health')
         assert u.wait_on_action(action_id), "HEALTH_OK"
 
+    def test_420_show_disk_free_action(self):
+        """Verify show-disk-free"""
+        u.log.debug("Testing show-disk-free")
+        if self._get_openstack_release() < self.trusty_kilo:
+            u.log.info(
+                "show-disk-free only supported in >=kilo, skipping")
+            return
+        sentry_unit = self.ceph0_sentry
+        action_id = u.run_action(sentry_unit,
+                                 'show-disk-free',
+                                 params={'format': 'json'})
+        assert u.wait_on_action(action_id), "Show-disk-free action failed."
+        data = amulet.actions.get_action_output(action_id, full_output=True)
+        assert data.get(u"status") == "completed", "Show-disk-free failed"
+        message = data.get(u"results").get(u"message")
+        assert message is not None
+        jsonout = json.loads(message.strip())
+        nodes = jsonout.get(u"nodes")
+        assert nodes is not None, "Show-disk-free: no 'nodes' elem"
+        assert len(nodes) > 0, "Show-disk-free action: 0 nodes"
+
     def test_499_ceph_cmds_exit_zero(self):
         """Check basic functionality of ceph cli commands against
         all ceph units."""