SLP Duplication to LTO -5 Tapes speed very slow

Hi

I am using NEtbackup Appliance 5220 with 2.5.1. The configuration is 4 Fibre Connected LTO-5 Tape Drives with MSDP pool of 32 TB.  I have created SLPs to first backup data to MSDP pool and then to Tapes.

The first problem is i cant see the speed when data s written from MSDP pool to tapes via SLP. The java console doesnt shoow anything in job details under activity monitor. So, i am looking int bpdb logs which shows me a speed of not more than 70MB/s. I havae arround 30 TB of data which goes to tape during  weekends via FUll Backups.

I need to do some capacity planning, so it i very important for me to understand this.

Please help..