<architecture> (RAIS) The use of multiple servers to provide the same service in such a way that service will still be available if one or more of the servers fails. The term may or may not imply some kind of load balancing between the servers. See cluster.
The term "RAIS" follows RAID, which describes schemes for resilient disk storage.
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Nearby terms: Redundant Array of Independent Disks « Redundant Array of Independent Drives « Redundant Array of Inexpensive Disks « Redundant Array of Inexpensive Servers » Redundant Arrays of Inexpensive Disks » red wire » red zone