Just thought I’d share my experience with the Netgear R6400 Router and its Readyshare Feature. I added a Seagate Expansion Desktop (external USB3.0) drive (5 Tb). I wanted to support both Windows and Mac OSX machines, so I ended up re-partitioning the Seagate drive using the Windows 10 (windows button+r, typing compmgmt.msc), clicking on Disk Management.
I created 3 partitions (2Tb NTFS, 2Tb empty, and 1 Tb NTFS). Then on a Mac, I used the disk utility to create a Mac HFS+ partition with the empty 2Tb empty. Just to test with Time Machine, I did a backup to this partition.
I then plugged the drive into the Netgear R6400. The drive ended up corrupting the HFS+ partition, so I brought it back to the Mac to repair. After repairing, it seems to work appropriately when plugged back into the Netgear.
So far so good! It does mean I have separate drives for Windows/Mac, but the drive is big enough that it works.