diff --git a/05-osm-usage.md b/05-osm-usage.md
index 507324da1ca4e352fbcb095db304ee9d4b34f886..4e7e2f1d1fea5ffbf7ae4405cfdff4838a52cdfc 100644
--- a/05-osm-usage.md
+++ b/05-osm-usage.md
@@ -573,6 +573,66 @@ An existing server-group may be passed as an instantiation parameter to be used
 
 Where the `id` of the `affinity-or-anti-affinity-group` is the one in the descriptor, and the `vim-affinity-group-id` is the guid of the existing server-group in Openstack to be used (instead of being created).
 
+### Keeping Persistent Volumes
+
+OSM supports three types of volumes: persistent, swap and ephemeral. Swap and ephemeral volumes are deleted together with the virtual machine. 
+Persistent volumes are used as an root disk or ordinary disk and could be kept in the Openstack Cloud environment upon virtual machine deletion by setting `keep-volume` flag `true` under `vdu-storage-requirements` in the VNFD. If the `keep-volume` is set to `false` or is not included in the descriptor, persistent volume is deleted together with virtual machine. A sample descriptor which keeps persistent volumes is given as follows:
+
+```yaml
+vnfd:
+  description: A basic VNF descriptor w/ one VDU and several volumes, keeping persistent volume
+  df:
+  - id: default-df
+    instantiation-level:
+    - id: default-instantiation-level
+      vdu-level:
+      - number-of-instances: 1
+        vdu-id: keep-persistent-vol-VM
+    vdu-profile:
+    - id: keep-persistent-vol-VM
+      min-number-of-instances: 1
+  id: keep_persistent-volumes-vnf
+  mgmt-cp: vnf-mgmt-ext
+  product-name: keep_persistent-volumes-vnf
+  vdu:
+  - id: keep-persistent-vol-VM
+    name: keep-persistent-vol-VM
+    sw-image-desc: ubuntu20.04
+    alternative-sw-image-desc:
+    - ubuntu20.04-aws
+    - ubuntu20.04-azure
+    virtual-compute-desc: keep-persistent-vol-VM-compute
+    virtual-storage-desc:
+    - root-volume
+    - persistent-volume
+    - ephemeral-volume
+  version: 1.0
+  virtual-storage-desc:
+  - id: root-volume
+    type-of-storage: persistent-storage
+    size-of-storage: 10
+    vdu-storage-requirements:
+      - key: keep-volume
+        value: 'true'
+  - id: persistent-volume
+    type-of-storage: persistent-storage
+    size-of-storage: 1
+    vdu-storage-requirements:
+      - key: keep-volume
+        value: 'true'
+  - id: ephemeral-volume
+    type-of-storage: ephemeral-storage
+    size-of-storage: 2
+```
+
+An existing persistent volume could be passed as an instantiation parameter by identifing the name of `volume` and `vim-volume-id` which is exact volume ID in the Openstack Cloud. `vim-volume-id` is only accepted as an instantiation parameter, it could not be provided in the descriptor. If the `vim-volume-id` is provided as a persistent volume, new persistent volume is not created, but reused. Existing volumes which are provided with `vim-volume-id` parameter are always kept without checking `keep-volume` flag, when the Network Service instance is deleted. The following example shows the syntax:
+
+```yaml
+--config '{ vnf: [ {member-vnf-index: vnf-persistent-volumes, vdu: [ {id: keep-persistent-vol-VM, volume: [{"name": root-volume, vim-volume-id: 53c485d0-7f32-4675-919d-a3ccaf655629}, {"name": persistent-volume, vim-volume-id: 4391a6af-6e00-470c-960f-73213840431e}] } ] } ] }'
+```
+
+Where the `name` of the `persistent-storage` is the one in the descriptor, and the `vim-volume-id` is the ID of volume in Openstack to be used (instead of being created).
+
 ## Understanding Day-1 and Day-2 Operations
 
 VNF configuration is done in three "days":