Slow websites at night

[mats]

I'm using the last ispconfig on my Debian (fully up2date) server.
It has a Intel(R) Xeon(R) CPU X3220 @ 2.40GHz and 4GB of memory.

My problem is that 1 of the websites I'm hosting is slowing down the complete webserver. when I disable the website everything is fast again.

But I can't find the cause of it, the servers CPU and MEM usage is normal (I think):

top - 20:58:28 up 116 days,  8:54,  1 user,  load average: 0.34, 0.46, 0.50
Tasks: 280 total,   2 running, 278 sleeping,   0 stopped,   0 zombie
Cpu(s):  4.5%us,  1.1%sy,  0.0%ni, 94.4%id,  0.0%wa,  0.0%hi,  0.0%si,  0.0%st
Mem:   3629296k total,  3490696k used,   138600k free,    68744k buffers
Swap:  2650684k total,      644k used,  2650040k free,  2462484k cached

It is only at night (18:00-22:00) when the site is having alot of visitors.
Stats for this month:
Monthly Statistics for October 2010
Total Hits 25720713
Total Files 13613694
Total Pages 2843599
Total Visits 370153
Total kB Files 244538092

Can you help me troubleshoot this problem? cause my websites are so slow at night... (other functions on the server like ssh and teamspeak are working fine).

[edge]

Sounds like a bandwidth problem.
What is your bandwidth (up and down)?

[mats]

100mbit and when its slow I can still download a 1000mb.bin file with wget with 11mb/s.
And downloading from the http goes about 5mb/s (But takes a while before it starts).

[edge]

Is the upload also 100mbit?

[mats]

Yes its in a datacenter in amsterdam ( colocation)

[edge]

I did have this problem also a long time ago.
Not sure if this will work for you, but after tweaking apache I managed to get the troubled server working better.
see: http://www.howtoforge.com/forums/showthread.php?t=9303

Read this for "Configuring Apache for Maximum Performance"
http://www.howtoforge.com/configurin...um_performance

PS. Some of my servers are also located in Amsterdam (transIP)

Groet.