Kdd hogs 93% of my network

I have a WD MyCloud Home and am using WD Discovery. I have a mapped drive Z: and whenever I copy a file onto the mapped drive it almost completely blocks all other network traffic to the PC. Task manager reports 93% against kdd. Is there an alternative? The drive is physically in the same building (our house) as the PC, on the same local network. So, whilst copying, forget trying to access web sites, email, etc.

How is your home network setup and what router do you own?

Issue was resolved. A faulty network hub was identified as the cause in the end.