Sql restore performance issue

Hi Experts,

  i am restoring Sql database of size 800gb with filestream enabled. The actial .ldf & .mdf file sie is just 10gb each and rest all filesream data which contains millions of small files chunks. When i start the restore, it is giving speed of 30-35mb/s and after 650gb the speed becomes 100kb or below.it was running 3 days but restore did not complete. I tried with LAN, FT, direct cross cable lan but same result. Restoring from appliance media server. nbu 7.6.0.2

Any idea what would be the go forward ?