Mirroring

1. Writing duplicate data to more than one device (usually two hard disks), in order to protect against loss of data in the event of device failure. This technique may be implemented in either hardware (sharing a disk controller and cables) or in software. It is a common feature of RAID systems. When this technique is used with magnetic tape storage systems, it is usually called 'twinning'.
   
   A less expensive alternative, which only limits the amount of data loss (rather than eliminating the risk entirely), is to make regular backups from a single disk to magnetic tape.
2. An archive or web site which keeps a copy of some or all of the files at another site so as to make them available more quickly to local users and to reduce the load on the source site. Such mirroring is usually done for particular directories or files on a specific remote server, as opposed to a cache or proxy server which keeps copies of everything that has been requested through it.

   
   

   *** The Information Security Glossary ***