try to use slider for disksize

app/UI/Disk/Forms/CreateForm.php

@@ -52,8 +52,8 @@ class CreateForm extends BaseForm implements ClientArea
     private function initFields()
     {
         //size
-        $field = new Range('size', 5, $this->resourceManager->disk()->free());
         $resourceManager = new ResourceManager();
+        $field = new Range('size', 5, $this->resourceManager->disk()->free());
         $field->addValidator(new NumberValidator($resourceManager->disk()->getMin(),$resourceManager->disk()->free(), true));
         $field->setDefaultValue($this->configuration()->serverDiskSize->min);
         $this->addField($field);