A copy of a site with some content differences to target particular keywords. Not a recommended strategy as it can trigger a penalty or ban.
A mirror site is an exact replica of another Internet site. A mirror site is used to reduce network traffic or improve the availability of the original site. These are useful when the original site generates too much traffic for a single server to support.
Mirror sites can be defined as servers in different locations with identical i.e. mirrored content. This may be due to the reason that bandwidth on the Internet can vary wildly between computers on different providers, countries or continents. Mirroring allows the viewers to select the server that at any given moment provides the best connection. If a particular server is currently unavailable, another mirror server is still there.
This allows faster downloads for users at a specific geographical location. For e.g. a U.S. server could be mirrored in the UK, allowing British Internet users to download content faster from the local British server than from the original American one.
This technique provides access to otherwise unavailable information. This can be understood by considering the case, when the popular Google search engine was banned in 2002 by the People’s Republic of China. Mirror elgooG (for Google) was used as a way of effectively circumventing the ban.
Common ones are:
Rsync: a software application for UNIX systems which synchronizes files and directories from one location to another while minimizing data transfer using delta encoding. One of the most important features of rsync not found in most similar programs/protocols is that the mirroring takes place with only one transmission in each direction. It can copy /display directory contents and copy files. This is done optionally using compression and recursion.
CVSup: is a program that synchronizes files and directories from one location to another while minimizing data transfer using the file-type specific delta encoding when appropriate. This program was designed for keeping source code repositories – such as CVS – synchronized. However, this has been extended to support synchronizing any type of file