This page handles mirrors in the sense of remote copies of extranet servers, not reflective surfaces.

In order to keep the extranet running smoothly in the face of collosal communication lag, most data that is expected to be requested over a large area is stored on many slaved mirror servers which are updated with a full copy of the master server periodically.

The upside of this is that the time required to access the data is limited to the time needed to fetch it from the nearest mirror as opposed to the time required to fetch it from the master server, something that can cut months of the loading time, especially if there is a mirror within the same starnet.

The downside is that the data can be out-of-date and that the cost of the data will be higher so the mirror host can turn a profit or at least maintain the mirror.