Specifications
DATA CENTER BEST PRACTICES
SAN Design and Best Practices 30 of 84
– M-Series (legacy McDATA) switches: Similar to legacy switches, the presence of M-Series switches
anywhere in the SAN environment impacts the features that are supported and, depending on the
platform and rmware version, may have other impacts as well.
– Advanced SAN application/features: If you are considering implementing advanced SAN applications and/
or features, the key factor is support (or compatibility) of the application on the SAN switch platforms
being considered, as well as the ability to support those features across FCR.
•Projected inter-fabric trafc patterns:
– Quantity (bandwidth utilization): You should provision a sufcient number of IFLs between each edge
and the backbone to accommodate the projected trafc (at peak load) to and from each edge fabric. In
addition, you should provision enough ISLs within the backbone to accommodate the projected trafc (at
peak load) that will traverse the backbone.
– Bursty versus continuous trafc: Bursty trafc is more forgiving than continuous trafc, since it generally
handles temporary spikes in latency (unavailability of bandwidth). If the trafc pattern is largely made up
of continuous streams of data, then provision extra bandwidth.
•Small versus large frame size: Fibre Channel is a high-speed, low-latency protocol. It relies, however, on buffer-
to-buffer credits to handle ow control. This mechanism is a fundamental part of the Fibre Channel standard
and ensures lossless connections. Thus, a series of 100 small frames uses the same number of buffers
as a series of 100 large frames. Large frames, on the other hand, use more bandwidth. In other words,
a large amount of small-frame trafc can fully utilize available buffers, while consuming only a very small
amount of available bandwidth. Therefore, you need to consider not only bandwidth, but also the typical frame
size. If the bulk of frames are expected to be smaller in size, then additional links and/or buffers should
be allocated to the paths that will be handling those smaller frame I/O patterns. Pay extra attention to this
type of congestion, because backbones can become congested and adversely impact the performance of all
connected edge fabrics. When in doubt, overprovision IFLs.
•Distance (location of fabrics): The distance between the end-points of the data transmission is an issue of
providing adequate buffers for the projected trafc, and all of the potential trafc ows that might traverse
the long-distance link(s) need to be considered. Given that long-distance solutions generally already have
increased latency (simple physics of time to cover distance), it is important that long-distance links be
overprovisioned for capacity, such that unexpected spikes do not adversely impact the data ow or, potentially,
the entire network.
•Virtual Fabrics (VF): If VF is enabled, the base switch is like a backbone switch, and a base fabric is like a
backbone fabric. All switches in a backbone fabric must have the same backbone fabric ID, which must be
unique from the edge fabric.
Note: The VF Fabric ID is also the backbone, and Fabric ID and EX_Ports and VEX_Ports can be configured only on
the base switch.
•Zoning: Trafc Isolation (TI) zones and FCR: Some VE_Port-based features, such as tape pipelining, require the
request and corresponding response trafc to traverse the same VE_Port tunnel across the MetaSAN. Use TI
Zones to ensure that the request and response traverse the same VE_Port tunnel; you must set up TI Zones
in the edge and backbone fabrics. In addition to setting up TI Zones, you must also ensure that the devices
are in an LSAN zone so that they can communicate with each other. If failover is enabled and the TI path is
not available, an alternate path is used. If failover is disabled and the TI path is not available, then devices
are not imported.
•A potential for growth exists in the following:
– Number of fabrics: If the number of fabrics is likely to increase, then deploy backbone fabrics such that
they can readily accommodate additional edge fabrics and additional trafc loads.