Specifications

DATA CENTER BEST PRACTICES

SAN Design and Best Practices 18 of 84

Another method is to assign host ports to storage ports based on capacity. The intended result is a small

number of high-capacity hosts and a larger number of low-capacity servers assigned to each storage port,

thus distributing the load across multiple storage ports. Figure 14 shows the impact of the two different LUN

provisioning strategies described above. Notice that there is a huge diffenence between the fan-in to the storage

port, based on the number of LUNs provisioned behind the port.

fig14_SAN_Design

Fabric

port

Storage

port

LUN

LUN-based provisioning

Disk array

50 connections

Fabric

port

Storage

port

LUN

Capacity-based provisioning

5 connections

Figure 14. Two different LUN provisioning strategies.

Regardless of the method used to determine the fan-In/fan-out ratios, port monitoring should be used to

determine actual utilization and what adjustments, if any, should be made. In addition, ongoing monitoring

provides useful heuristic data for effective expansion and efcient assignment of existing storage ports. For

determining the device-to-ISL fan-in ratio, a simple calculation method works best: the storage port should not

be oversubscribed into the core (Example: an 8 Gbps storage port should have an 8 Gbps pipe into the core).