Increased port capacity and redundancy are popular features of Fibre Channel SANs. The elimination of a single point of failure in the host-storage relationship is significant and increases business availability and uptime. Figure 2-1 illustrates the concept of a single point of failure on an application in a DAS environment.
Figure 2-1. Sample DAS Configuration
In Figure 2-1, two non-clustered hosts share a single storage frame without the benefit of a SAN. If the application residing on Host 1 is not mirrored on Host 2, and the link between Host 1 and the storage array is dropped, then the application cannot access its storage. There is no way for the disk devices attached to Host 1 to be shared with Host 2; therefore, the application on Host 1 is prevented from starting on Host 2. Similarly, if Host 1 goes down, there is no way to bring up the application from Host 1 on Host 2. This many-to-one configuration does not offer high availability or data resiliency.Figure 2-2 shows the elimination of the single point of failure in the same environment with the installation of two 16-port Fibre Channel fabric switches and the creation of a SAN.
Figure 2-2. SAN Configuration Examples
[1] This figure works out to roughly $121,141.98 per minute of downtime or $2,019.03 per secondnot a trivial amount of money. These numbers highlight the well-known fact that availability affects revenue.
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