how do I know what server I'm on? is it shown somewhere in the DH control panel?
It should have said in your "welcome email", but you can check on the Control Panel. A good place to get a lot of information is by clicking "Account Status" in the top right-hand corner of the panel (including your server).
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ping your domain name.If you have shell access, ssh to your domain name. It may show host name, or you can give hostname command.