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Mirroring files distributed by http or ftp servers consists in making regular copies of the files from the master source to another distant server. The copying is often carried out on a daily basis, at off-peak times and arranged to transfer only those files which have been changed since the previous copying operation.
Mirroring is useful in circumstances where the local (regional or national) network is fast but the connections beyond this fast region are considerably slower. The average number of times a file is read from the mirror server between modifications should be as large as possible. This implies that the larger the number of users of the mirror server and the slower the rate of modification of the files the more efficient and cost-beneficial the mirror server becomes.
The principal beneficiaries of the installation of a mirror server are the local users since the speed of delivery of information is increased for them. However the existence of mirror servers also diminishes the number of accesses to the master server, decreasing its work load, and further reduces the trafic on the overcongested, critically slow sections of the network. Nevertheless the onus for the setting up of mirror sites lies primarily within the local, regional or national context.
The following mirror software is public domain and very easy to configure. Please note that mirror-2.3 uses Perl 4.x whereas mirror-2.5 needs Perl 5.x. The latest version of mirror is available from:
The IUCr runs a pan-crystallography server system through a network of mirrors world-wide. In the section Mirroring a Pan-Crystallography Server the stylistic and naming conventions for information providers and certain configuration parameters for mirror managers are described. Fuller details are available from the IUCr's Research and Development Officer.