I've noticed that if I gunzip a file in /tmp, it sends the server load average to about 60. (/home is fast; only /tmp is slow.) That probably doesn't have anything to do with anything, but I've never seen it before.
I haven't quite figured out the infrastructure, but there seems to be a number of servers (or at least IP addresses) involved in delivering a page.
- There's your main server.
- Your web site has a different IP address from the main server. In fact, every subdomain is potentially served from a different IP. They're usually named basic-something.yourserver.dreamhost.com. They seem to re-use the same names across all servers. I don't know how this works.
- There's a filer, which is where your files are actually stored.
- There's probably a MySQL server. (And perhaps these use the filers too... and maybe some other layer of abstraction, judging by the way they're named.)
... not to mention the hardware involved in connecting all these devices.
It might help to see if people who are experiencing performance problems share anything in common.
My sites all work fine. (They use databases, but not heavily.)