mirror

1. hardware, storage 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 diskcontroller and cables) or in software. It is a common

feature of RAID systems.

Several operating systems support software disk mirroring or

disk-duplexing, e.g. Novell NetWare.

See also Redundant Array of Independent Disks.

Interestingly, when this technique is used with magnetictape storage systems, it is usually called "twinning".

A less expensive alternative, which only limits the amount of

data loss, is to make regular backups from a single disk to

magnetic tape.

2. networking An archive site or web site which keeps a

copy of some or all files at another site so as to make them

more quickly available to local users and to reduce the load

on the source site. Such mirroring is usually done for

specific whole directories or files on a specific remote

server as opposed to a cache or proxy server which keeps

copies of everything that is requested via it.

For example, src.doc.ic.ac.uk is the main UK mirror for the

GNU archive at gnu.org. There are also several

mirrors of this dictionary.

(1998-06-11)