After a long research on how to get the storage node working on WD My Cloud Ultra Ex2 i found the following approach working for me i would like to share a few points.
1 I used raspberry pi 4. As is it not easy to install docker daemon on the NAS itself
2. I mounted the nas share to the pi. I attempted with three protocols NFS, CIFS/SMB iscsi.
3. With NFS and CIFS, it is easier to set up, but the MySQL database will not be happy with it and will cause some issues. With iscsi things work better. but the setup is more complicated as you need to create a volume, formate it, and mount it to the pi.