A fan-out ratio is the relationship in quantity between a single port on a storage device and the number of servers that are attached to it.
It is important to know the fan-out ratio in a storage area network (SAN ) design so that each server gets optimal access to storage resources. When the fan-out ratio is high and the storage array becomes overloaded, application performance will be affected negatively. Too low a low fan-out ratio, however, results in an uneconomic use of storage.
Key factors in deciding the optimum fan-out ratio are server host bus adapter (HBA) queue depth, storage device input/output (IOPS) and port throughput.
This was last updated in March 2012
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