Most NAS brands run Linux as a backbone, so it is usually easy to recover data by connecting the disks from the NAS to a system running Linux.
IMPORTANT: Remember the order in which the disks were arranged in the NAS; as this may be needed for the recovery process.
Prepare a PC with enough hard drive slots available to install the hard drives from your NAS.
NOTE: Ensure the file system running on the hard drives of your NAS are EXT4 or Btrfs.
If the NAS only had a single disk, then this disk should be immediately accessible and no further steps in these instructions are needed.
sudo apt-get install mdadm
NOTE: When prompted for Postfix Configuration.
sudo apt-get install lvm2
NOTE: This is needed for vgchange.
sudo mdadm -Asf && vgchange -ay
NOTE: The files on the hard disks should be accessible.