McDATA StorageWorks 64 - SAN Director Switch Planning Manual page 200

Implementing SAN Internetworking Solutions
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McDATA Products in a SAN Environment - Planning Manual
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— FastWrite technology - Enable FastWrite technology to reduce
protocol overhead for extended-distance write transactions.
The technology is very efficient over long distances with large
write transactions (such as SDR applications).
— Bandwidth management - Enable QoS processing to
guarantee bandwidth over a shared link. QoS subdivides port
buffers into multiple queues, each with one or more associated
drop thresholds. Multiple queues and drop thresholds allow
the switch to prioritize output when faced with congestion.
3. Minimize fabric hop count - The maximum supported hop count
in a fabric is three. Because the E_Port-to-R_Port ISL between a
fabric element and SAN router counts as a hop, SAN routing
connectivity is limited to two-hop fabrics. A remotely connected
fabric does not add to the hop count of a local fabric; remote
devices appear connected to the SAN router using proxy
Domain_IDs 30 and 31. The best practice is to directly connect a
SAN router to server and storage ports. However, SAN router
connectivity through a fabric element is practical if the topology
is required for scalability.
4. Configure dual storage array controllers - Storage device OEMs
provide at least two controllers per storage array. Although SDR
and ADR applications work with a single controller, use at least
two controllers to provide high availability. Each controller has
multiple Fibre Channel N_Ports that can be assigned to the SDR
or ADR application. Most data replication software can load
balance and initiate failover across the controllers.
5. Implement parallel-path architecture - It is recommended to
configure redundant, parallel extended-distance links. It is also
important to keep the links as homogeneous as possible. Some
data replication applications are sensitive to path differences and
decrease performance to the lowest common denominator. The
best practice is to configure a dual-link architecture with similar
paths (bandwidth and latency), through which SDR or ADR
software performs load balancing and failover.
6. Do not implement IP network failover - Implement extended-
distance link failover through the data replication software, not
the IP network. Many SDR and ADR software OEMs do not
support IP network link failover.