As400 to DD VTL Backup

Hi,

We have DD6800 and we are trying to push the backup form AS400 to DD via VTL. Our DD is connected to AS400 vi SAN fabric. In there we have seen a backup slowness. When we running the 4TB backup from AS400 to DD it will took ~2h 40min and when we running the backup on AS400 to tape library it will took  ~1h 10min. Then we have monitored the data transfer speed of the particular ports on the SAN SW. When the backup is running form AS400 to DD data transfer speed on the particular ports are ~300-400M and when the backup is running the AS400 to Tape Library data transfer speed is ~400 - 600M. Therefore is this the case for the backup slowness in the DD VTL and how can we increase the transfer speed ? Is this need to be done form the AS400 end ? Pls advised.

Thanks,

Pasindu.