Replication

This technique duplicates the same data at the originating server at another place which is closer to the client so as to reduce latency. Replication is done by having a server (called mirror) store all or part of the files from one or more other servers, at their initiative. Then, the users may connect to the mirror instead of connecting to the primary server. This way the load on the primary servers can be reduced significantly, and the latency of file access may also be reduced if the user chooses an appropriate mirror.

Mirroring has been very popular for FTP servers for quite some time. However, serious drawbacks have been noticed:

Drawbacks

• Files are updated at periodic intervals; some may be out of date in the meanwhile
• Many mirrored files are not accessed frequently, therefore bandwidth for copying these files from the primary server and storage on the mirror, are wasted.
• It is the users responsibility to know which is the best mirror site; if they access an inappropriate site, the advantages of the method are nullified.
• The users cannot depend on a single mirror to access all the files they need.
• To be effective, a mirror should contain a good proportion of the frequently accessed files, be connected to the clients by high speed connections, and be well publicized.

The disadvantages of mirroring make it particularly uninteresting as a solution for reducing the load on servers with more dynamic content.