What can nginx log (logs disabled)?

Question

linux

Cheers to everyone. There is a linux / centos 6.5 server, software 10 RAID 4xTB, 32GB RAM, Intel i5 CPU
The performance of the server began to rest against the screw and overhead appeared. In atop-e busy sometimes jumps up to 70-80%, on average 30-40%, avio 4-8 ms. In iotop, nginx often flashes with a record on the screw up to 10 M / s.

error_log/access_log nginx-a logs go to /dev/null
All HTTP requests go to apache through nginx, REST API is implemented in php: inserting some information into the database and uploading files. Files are written to the screw (not to the database). I thought that the legs grow from here and remade the moment of saving files on a screw with a queue (2 threads per write) on a Java servlet. Nginx redirected to tomcat. Bottom line - didn't help. I will be very glad to any advice, the brain boils, thanks.

Answer 1

Turn on error_log there they would write what's what.
but in general, the problem is in proxy_buffering,
well, the logs need to be disabled not by the direction to /dev/null, but

access_log off;
error_log /dev/null crit;

You can also see where nginx writes (lsof to help)

Answer 2

If the log entry is written as,
replace with
and check again.

Answer 3

Or maybe it’s worth turning on the debug log and seeing if you still see the root of the problem in heaps of information