Network load
To evaluate remote backup performance, consider the following:
Small bursts of high network traffic for short durations can decrease data throughput rate. However, if the network traffic remains high, in particular if the MB/s in or MB/s out is frequently close to the network interface bandwidth, for example, 1.2GB/sec on a 10Gbps link, the network is probably the bottleneck. Try to schedule backups when network traffic is low. If your network is loaded, you may want to implement a secondary network which is dedicated to backup and restore traffic.
Alternatively, you may add additional network interfaces and use network bonding to join multiple network interfaces together to form a single interface to increase the single interface bandwidth.
Note also: to check the network, use FTP to transfer a large file (50 gigabytes or more) from the media server to the client and back again. Observe how long each operation takes. If moving the file in either direction takes significantly longer than the other, the network has a problem.