We had this issue copying large amounts of data to this Western Digital My Book Live Duo NAS.
It was mounted up on a Oracle Centos 6.5 VM but once we hit a file over 1GB in size, the machine would halt. Turns out we have to map the drive using the option protocol=udp like the following statement:
mount 192.168.1.45:/nfs /transport -o soft,timeo=60,intr,proto=udp
See, NFS mount by default uses TCP, but for Linux to work with this drive it needs to use UDP.