Specifications
DATA CENTER BEST PRACTICES
SAN Design and Best Practices 16 of 84
However, this approach does not scale well. Given the high-speed, low-latency nature of Fibre Channel,
attaching these host-target pairs on different switches does not mean that performance is adversely impacted.
Though trafc congestion is possible, it can be mitigated with proper provisioning of ISLs/UltraScale ICLs.
With current generation switches, locality is not required for performance or to reduce latencies. For mission-
critical applications, architects may want to localize the trafc when using Solid State Drives (SSDs) or in very
exceptional cases, particularly if the number of ISLs available is restricted or there is a concern for resiliency in
a multi-hop environment.
fig10_SAN_Design
Data
ow
Data
ow
Possible congestion
Data ow
Figure 10. Hosts and targets attached to different switches for ease of management and expansion.
One common scheme for scaling a core-edge topology is dividing the edge switches into a storage tier and a
host/initiator tier. This approach lends itself to ease of management as well as ease of expansion. In addition,
host and storage devices generally have different performance requirements, cost structures, and other factors
that can be readily accommodated by placing initiators and targets in different tiers.
The following topology provides a clearer distinction between the functional tiers.
fig11_SAN_Design
Host Tier
Storage Tier Tape Tier
Figure 11. Device type based edge-core-edge tiered topology.
Recommendations for device placement include:
•The best practice fabric topology is core-edge or edge-core-edge with tiered device connectivity, or full-mesh if
the port count is less than 2000 ports.
•Minimize the use of localized trafc patterns and, if possible, keep servers and storage connected to
separate switches.
•Select the appropriate optics (SWL/LWL/ELWL) to support the distance between switches and devices
and switches.