blockdev direct IO при отдаче видео с XFS (soft RAID) и ext4 (singl HDD)

[kozakd]

При нагрузке порядка 1500 конектов и
ближе к 2 Gbps 
ловлю в ps это blockdev_direct_IO
Есть варианты решения?

CenOS 6.0     2.6.32-71.29.1.el6.x86_64
RAM 16 GB
nginx 1.0.9


user  web;
worker_processes  1;
worker_rlimit_nofile 32000;
error_log  logs/error.log  info;
events {
    worker_connections  16000;
}


http {
    include       mime.types;
    default_type  application/octet-stream;
    
    server_tokens off;

    sendfile            on;
    tcp_nopush          on;
    
    tcp_nodelay         on;
    aio                 on;
    directio            4m;
    directio_alignment  4k;
    output_buffers  1   1m;


    keepalive_timeout   10;
    
    client_header_timeout       20;
    client_body_timeout         20;
    send_timeout                20s;
    resolver_timeout            0;
    reset_timedout_connection on;
    
    proxy_buffering off;
    
    open_file_cache          max=16000  inactive=10m;
    open_file_cache_valid    120m;
    open_file_cache_min_uses 10;
    open_file_cache_errors   off;

Posted at Nginx Forum: http://forum.nginx.org/read.php?21,218222,218222#msg-218222