[CentOS-mirror] How much space is needed to host a full mirror?

[Designer Peak]

My employer's executives attended the recent cPanel Conference, where they met some folks from the CentOS Project and were receptive to the suggestion that we host a public mirror. Most of the servers in our data center run CentOS.

How much disk space should I specify if we want to offer all versions and all architectures and even ISOs, for a conservative figure? Our private mirror holds only the repositories we regularly use, so I don't know how big the whole thing is. Depending on the size, I may have to pare down the offering.