Backup/restore throughput

Hi,

I have Master, Media and Client : Linux RedHat 6.1 , nbu 7.5.0.6
Tape Library with LT06 media and drives.
Mater-Media-Client connected on 10Gb Lan, Master-Tape Library connetected on SAN switch with 8Gb speed.
Backup Policy configured with 4 multiplexing.

I get backup throughput at 140Mbps but when doing restore I only get 10-13Mbps.
This is very less throughput .

Please suggest, How to check where is the bottleneck and how to improve it?

Thanks,