One can copy the data from one My Cloud to another by simply dragging and dropping files between the two using Windows File Explorer or Mac Finder. Just like you do copying files between your computer and the My Cloud. It is best to do this from a computer that is connected by Ethernet (wired) to the same gigabit capable router or network switch that both My Cloud units are connected to. Trying to copy large files using WiFi typically will take longer. Or one can see if they can copy the files to the new My Cloud using OS3 My Cloud Desktop’s Safepoint / Backup feature. Or one can attach a USB hard drive to the old My Cloud, copy files to it, then move that USB hard drive to the new My Cloud and copy the files from the USB hard drive to the new My Cloud. Or one can see if they can use SSH to issue Linux Rsync command to copy files from one My Cloud to another. One can use the forum search feature (magnifying glass icon top right) to find many past discussions and examples of how to use Rsync to copy files/data from one My Cloud to another on the local network.
The question of how to copy data between two My Cloud is also discussed in various recent posts including the two discussions right under your post.
WD is ending remote access support for OS3 My Cloud units, one will still be able to access their local network OS3 My Cloud just as they currently do using Windows File Explorer, Mac Finder or any other file manager program or app on a local network computer or device. For local network access nothing should be changing. One will still be able to “map” their OS3 My Cloud Shares just as they do today.
How to map a My Cloud or NAS device on Windows
https://support-en.wd.com/app/answers/detail/a_id/9323
How To Map a My Cloud or NAS Device on macOS
https://support-en.wd.com/app/answers/detail/a_id/24148
