With OpenKM you can export all your folder structures and documents to your server disk. Log as okmAdmin and go to Administration > Repository Export. This operation is really easy. You simply put your OpenKM origin path and your operating system destination folder path.
The metadata and history checkboxes will enable the export of the document and folder metadata (author, creation date, etc.) and the whole document history. Sometimes you only may want the last version of the document, so don't need to check this option.