Redhat 7.3 with Ensim, why downtime?

why do I have some downtime/slow

[zeus]

Every day I have a few min. sometimes hours of downtime/slow periode, I just dont know why, because when the site is online everything is quick and stable.

Im not that much into servers and ensim, but we all have to start, but what could be my problem, I have closed the analog logs and normal stats I have it 4 times a day.

I get about 30.000 unique visits and therealot of pictures involved so I use about 400GB a month, but I can use 700GB bandwidth.