Importance

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Abstract

Embodiments of the invention are concerned with data distribution apparatus, for use on each of a plurality of machines in distributing a set of data over a network amongst said machines. The apparatus comprises: i) multicast apparatus for use in multicasting said set of data over the network for receipt by others of said machines; and ii) a data retrieval arrangement for use in retrieving data from a set of data previously multicast by at least one of said machines, and supplying retrieved data to the multicast apparatus for use in multicasting the retrieved data over the network to others of the plurality of machines, wherein more than one of said plurality of machines is enabled to act as a multicast source in distributing the set of data over the network. In embodiments of the invention, a first machine is elected as download master and multicasts downloaded data, via a group address, to the networked machines. Each machine receiving the multicast data monitors the data blocks received and, if a machine has received an incomplete set, for example because it came online late or as a result of unreliability, it can access a shared cache of another machine having a more complete set. Such a machine then starts a secondary multicast so that other machines can also complete their sets. Only one machine provides a secondary multicast at one time, to prevent high traffic in the network. While the download master is still downloading, the secondary multicast function is cycled around amongst the networked machines to avoid overload of any one machine.

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First Claim