Mirror

In computing, a mirror is an exact copy of a data set. On the Internet, a mirror site is an exact copy of another Internet site. Mirror sites are most commonly used to provide multiple sources of the same information, and are of particular value as a way of providing reliable access to large downloads. Mirroring is a type of file synchronization.
A live mirror is automatically updated as soon as the original is changed.
A good example of mirroring is the well-known SourceForge.net website. The basis of the Sourceforge concept is, primarily, the hosting of open-source software projects, but secondarily the use of many different locations to achieve one goal: to maintain download availability to the user. Many innovative computer projects host their sites and software on SourceForge, which provides mirrors in several countries, from Dublin, Ireland to Tokyo, Japan.
Examples of even larger mirrored networks include those of the Debian and FreeBSD software projects. The encyclopedia Wikipedia is mirrored at numerous locations.
Examples of free file mirroring sites are MassMirror, Sharebee.com. They allow anyone to mirror any file.
Disk mirroring:- In data storage, disk mirroring or RAID1 is the replication of logical disk volumes onto separate physical hard disks in real time to ensure continuous availability. A mirrored volume is a complete logical representation of separate volume copies.
In a Disaster Recovery context, mirroring data over long distance is referred to as storage replication. Depending on the technologies used, replication can be performed synchronously, asynchronously, semi-synchronously, or point-in-time. Replication is enabled via microcode on the disk array controller or via server software. It is typically a proprietary solution, not compatible between various storage vendors.