I (and about everybody else) recommend to use the VirtIO driver for your virtual hard disk. I assume you did that, because otherwise Windows 10 would have detected the device out of the box. You need a separate driver for that.
You can get the latest one from here:
Download the ISO file and create a second CDROM device for your VM. Additionally make sure that your HDD device is set to VirtIO and a blocksize of 512 instead of the value "default".
Boot, then when you get into the partition dialog, navigate to the "load driver" or whatever that is called. Should not be that difficult. Then navigate to the second CDROM, E: probably and load the 64 bit RedHat VirtIO SCSI driver. Probably the NetKVM (network) driver, too.
You should be able to partition and use your virtual disk afterwards.
After installation is complete, just remove the CDROM devices entirely to boot to Windows.