diff --git a/app/models/vm_or_template/operations/configuration.rb b/app/models/vm_or_template/operations/configuration.rb
index 66b2beeface..3c33bdd58d9 100644
--- a/app/models/vm_or_template/operations/configuration.rb
+++ b/app/models/vm_or_template/operations/configuration.rb
@@ -74,8 +74,10 @@ def disconnect_floppies
   def raw_add_disk(disk_name, disk_size_mb, options = {})
     raise _("VM has no EMS, unable to add disk") unless ext_management_system
     if options[:datastore]
-      datastore = Storage.find_by(:name => options[:datastore])
-      raise _("Data Store does not exist, unable to add disk") unless datastore
+      datastore = ext_management_system.hosts.collect do |h|
+        h.writable_storages.find_by(:name => options[:datastore])
+      end.uniq.compact.first
+      raise _("Datastore does not exist or cannot be accessed, unable to add disk") unless datastore
     end
 
     run_command_via_parent(:vm_add_disk, :diskName => disk_name, :diskSize => disk_size_mb,
diff --git a/spec/models/vm_or_template/operations/configuration_spec.rb b/spec/models/vm_or_template/operations/configuration_spec.rb
new file mode 100644
index 00000000000..0395f5e1fdb
--- /dev/null
+++ b/spec/models/vm_or_template/operations/configuration_spec.rb
@@ -0,0 +1,59 @@
+describe VmOrTemplate::Operations::Configuration do
+  context "#raw_add_disk" do
+    let(:disk_name) { "abc" }
+    let(:disk_size) { "123" }
+
+    context "when ext_management_system does not exist" do
+      let(:vm) { FactoryGirl.create(:vm_or_template) }
+
+      it "raises an exception when does not find ext_management_system" do
+        message = "VM has no EMS, unable to add disk"
+        expect { vm.raw_add_disk(disk_name, disk_size, {}) }.to raise_error(message)
+      end
+    end
+
+    context "when ext_management_system exists" do
+      let(:vm) { FactoryGirl.create(:vm_or_template, :ext_management_system => ems) }
+      let(:ems) { FactoryGirl.create(:ext_management_system) }
+      let(:storage_name) { "test_storage" }
+      let(:storage) { FactoryGirl.create(:storage, :name => storage_name) }
+      let(:storages) { double("storages") }
+      let(:host) { double("host", :writable_storages => storages) }
+      let(:hosts) { [host] }
+
+      before do
+        allow(ems).to receive(:hosts).and_return(hosts)
+      end
+
+      context "when storage exists" do
+        it "adds a disk on the storage" do
+          allow(storages).to receive(:find_by).with(:name => storage_name).and_return(storage)
+          allow(ems).to receive(:authentication_status_ok?).and_return(true)
+          allow(ems).to receive(:vm_add_disk)
+
+          expected_options = {
+            :diskName        => disk_name,
+            :diskSize        => disk_size,
+            :thinProvisioned => nil,
+            :dependent       => nil,
+            :persistent      => nil,
+            :bootable        => nil,
+            :datastore       => storage,
+            :interface       => nil
+          }
+          expect(vm).to receive(:run_command_via_parent).with(:vm_add_disk, expected_options).once
+          vm.raw_add_disk(disk_name, disk_size, :datastore => storage_name)
+        end
+      end
+
+      context "when storage does not exist" do
+        it "raises an exception when doesn't find storage by its name" do
+          allow(storages).to receive(:find_by).with(:name => storage_name).and_return(nil)
+
+          message = "Datastore does not exist or cannot be accessed, unable to add disk"
+          expect { vm.raw_add_disk(disk_name, disk_size, :datastore => storage_name) }.to raise_error(message)
+        end
+      end
+    end
+  end
+end