How to connect my book and my cloud

i have a my cloud with 3 tb storage and a my book with 4 tb storage.
When I connect my book with my cloud, the my cloud turns a solid red.
Both the storage devices have their own power sources
i also tried formatting the my book to NTFS but to no avail
what should i do?

Couple of suggestions. Try using a USB hub between the My Book and My Cloud.

Use a different USB cable to connect the My Book to the USB port on the My Cloud.

Check the My Book partition layout and format. The My Cloud sometimes has problems accessing a USB hard drive with more than one partition, especially if the data partition is the second partition on the hard drive.

Try using a Windows computer (if you haven’t already) to format the My Book for NTFS.

Not sure about the problems with two partitions. I have a thumb drive with two partitions.
one formatted as Fat32 nd the other formatted as ext3. I use it to boot from the thumb drive.
It boots from the Fat32 partition and after the boot both partitions are mounted.

The My Cloud gets a bit goofy some times with USB drives. I have no problems with flash drives. USB hard drives are another story. Had one USB 3.0 hard drive (from Toshiba) that had two partitions on it. The second partition was the data partition and was formatted for NTFS. The first gen My Cloud wouldn’t recognize it. Seemed it was picking up the first partition as the main partition rather than the second partition. Have a thread/post or two in the past discussing it. Only way to get the My Cloud to recognize the drive was to remove all partitions, create one single partition and format it for NTFS.

And on a side note since it’s related to the USB port, while the My Cloud documentation claims it can support up to seven USB devices. It appears having anything over four or five devices and the My Cloud has trouble recognizing devices/drives.