NFS 0-byte problem

[kernelheaders]

Hello all ,

We're using nginx 1.1.6 ver. 5 server connected NetApp storage via NFS .
(/var/www )

Sometimes 1 or 2 server return cache size 0-byte and don't answer http
request. Other 3 server working well .  
If i restarted nginx or delete cache file , 0-byte problem resolve.
 

Example service conf :

upstream upstream.test.com {
        server 1.1.1.1:80;
        server 2.2.2.2:80 backup;
        server 3.3.3.3:80 backup;
}


server {
        listen       80;
        server_name     video.test.com;
        access_log   off;

        location / {
                proxy_pass         http://upstream.test.com;
                proxy_ignore_headers Expires Cache-Control Set-Cookie;
                proxy_cache_valid  200 30d;
                proxy_cache     $host;
                proxy_connect_timeout 5;
                proxy_read_timeout 10;
                proxy_next_upstream error timeout http_500 http_502
http_503 http_504 http_404;
                set $maincache  "main-a:";
                proxy_cache_key         $maincache$host$uri;
                proxy_redirect     off;
                proxy_set_header   Host             $proxy_host;
                proxy_max_temp_file_size 0;
                proxy_hide_header Cache-Control;
                proxy_hide_header X-Powered-By;
                proxy_hide_header X-AspNet-Version;
                expires         30d;

        }

        location ~ /delete(/.*) {
                allow                   5.5.5.5;
                deny                    all;
                set $deluri $1;
                set $maincache  "main-a:";
                proxy_cache_purge       $host   $maincache$host$deluri;
        }
}


Where i'm mising ?

Thanks

Posted at Nginx Forum: http://forum.nginx.org/read.php?2,217496,217496#msg-217496