Copying data to a new NAS from an old NAS - Fastest Method

Hi All,

I have just bitten the bullet and spent, in my terms, serious lucre on a new Synology DS1621+ NAS with 6x 4TB hard drives.
The DS is all setup as a single drive in Synology Hybrid RAID mode and I now start the process of copying data from a Zyxel across to the DS.

What is the most speed efficient way of doing this? The RAID1 file structure on the Zyxel has separate top level folders for Movies, TV, Music and Data folders for each household user that I'm copying across using a drag and drop method from within the DSM Interface.

Is this the best method? Any advice would be most welcome.