Slow transfer rate between Symantec server and JD Edwards

Dear Support, 

I am running a Symantec job for Enterprise JD Edward to backup 1.2 TB the back was fine from 1 year, until suddenly the ratio rate of data became 660MB/Min, it was before more than 4GB. 

I have the enterprise data in an HP MSA 2040 data store connected with an original HP fiber Multimode OM3 LCLC FC, I am confused cos all other servers are successfully backed up without any delay and with a transfer rate around 3.5 GB, note that these servers are in another data store.

i have attached two images one with high transfer rate and the second with lawer