Technology for maintaining a backup of namespace metadata of an expandable storage volume is disclosed. In various embodiments, the expandable storage volume backs up metadata of a namespace constituent volume of the expandable storage volume into a namespace mirror volume. The namespace constituent volume is responsible for storing the metadata for data objects stored in multiple data constituent volumes of the expandable storage volume. In response to a signal indicating that the namespace constituent volume is unavailable, the namespace mirror volume replaces the role of the namespace constituent volume. The new namespace constituent volume continues to provide metadata for a data object of the data objects in response to an operation request for the data object.