McDATA StorageWorks 2/140 - Director Switch Planning Manual page 198

Implementing SAN Internetworking Solutions
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McDATA Products in a SAN Environment - Planning Manual
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— Jumbo frames - To prevent fragmentation of Fibre Channel
frames into multiple IP datagrams, enable jumbo frames to
increase the data packet size from 1,500 bytes to
approximately 9,000 bytes. Ensure the technology is
supported by all IP network equipment in the data link.
— 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 RDR/S 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
RDR/S and RDR/A 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 RDR/S or RDR/A application. Most remote 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
remote 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 RDR/S or RDR/A software performs load balancing and
failover.