[webizen]

Originally Posted by GiedriusQ

...
3x120GB SSD (2 in software raid0, mounted on /files/ )
1Gbps network.
Debian Linux
2Core lite license.

Internet speed (IN) are around 200-300Mbps, OUT: 150-200Mbps
I think it's quiet too slow for such fast disk[?].
...

Your throughput is not necessarily slow given your 1Gbps network. It depends on what kind of file (smaller files lower the bandwidth usage due to TCP overhead) you serve and where the bottleneck is.

From the 'top -c' screenshot, looks like I/O is not the bottleneck. server load is not high. Real-time stats show you only have less than http 1000 connections used. However, your lsphp5 has max connection of 1000 which is too high. It should be set to 100~150 (in your case). so is the PHP_LSAPI_CHILDREN variable.