Strange server lags

If the server has more than 8-11 people he begins freezing on 0.5-1 second, and this is repeated again and again at regular intervals (29 - 32 seconds).

This is quite evident through HLSW:

http://s.zontwelg.com/images/gmod_server_lags.png

In this screenshot is not very visible, just a couple of people on the server.

Hardware:
SSD Vertex 4 128GB
AMD Phenom II x6 1075T (Upped to 3.7MHz)
24GB RAM DDR3
GIGABYTE-GA-970A-UD3

Addons:
WireMod
Falcos Prop Protection
Easy Precision 0.95
Adv Dupe 2
Stacker STool
Smart Freezer
Smart Welder
Unbreakable Tool
ULX

There are any suggestions? Thanks.

It’s possible that your network might not be able to handle that many people

Server is added on the LAN (in HLSW), and speed is:

What gamemode are you using

SandBox

Update:
Maybe problem in mysql server? Admin mod and FFP using mysql, and sending querys every 20 seconds to update user profiles.

If it’s a blocking action, then yes.

Okay, I reduced the number of queries and their frequency, is also a bit reconfigure mysql. So, i don’t see lags again.