There's no way, with an unhacked DNS-323, to get a RAID0/RAID1 disk configuration - if you do not use all of the available disk space in a RAID configuration, the remaining space is used in a linear JBOD configuration.
If you do not have a backup of your RAID0 volume, I would suggest you make that your first priority - RAID0 should never be used on a storage volume, and unfortunately I cannot offer suggestions to recover the data from your JBOD volume.