How optimizing nginx for local large files download.

[lienkai]

Hi,
    I have some dell860 servers.2GB ram,20Gbits network bandwidth.
    Twenty local large files(50M-2G) on the lighty server.
    Nginx online-testing,the single server make use of bandwidth 400M~550Mbits now.
    I wish optimizing nginx for bandwidth go up more than 1Gbits. 
    no-log,no-proxy,no-fcgi,only offer client soft download and patch download.
    How can do it resolve bandwidth low use?
    




                                T.kk