Specifications

DATA CENTER BEST PRACTICES
SAN Design and Best Practices 34 of 84
of latency at the receiving Condor3-based switch in order to decrypt and uncompress the frame. This results in a
total latency time of 12.4 microseconds, again not counting the link transit time.
Virtual Fabric Considerations (Encryption and Compression)
The E_Ports in the user-created Logical Switch, base switch, or default switch can support encryption and
compression. Both encryption and compression are supported on XISL ports, but not on LISL ports. If encryption
or compression is enabled and ports are being moved from one LS to another, it must be disabled prior to
moving from one LS to another.
In-Flight Encryption and Compression Guidelines
•It is supported on E_Ports and EX_Ports.
•ISL ports must be set to Long-Distance (LD) mode when compression is used.
•Twice the number of buffers should be allocated if compression is enabled for long distance, as frame sizes
may be half the size.
•If both compression and encryption are used, enable compression rst.
•When implementing ISL encryption, using multiple ISLs between the same switch pair requires that all ISLs be
congured for encryption—or none at all.
•No more than two ports on one ASIC can be congured with encryption, compression, or both when running
at 16 Gbps speed. With Brocade FOS v7.1, additional ports can be utilized for data encryption, data
compression, or both if running at lower than 16 Gbps speeds.
•Encryption is not compliant with Federal Information Processing Standards (FIPS).
DISTANCE EXTENSION TOPOLOGIES
For a complete DR solution, SANs are typically connected over metro or long-distance networks. In both cases,
path latency is critical for mirroring and replication solutions. For native Fibre Channel links, the amount of time
that a frame spends on the cable between two ports is negligible, since that aspect of the connection speed
is limited only by the speed of light. The speed of light in optics amounts to approximately 5 microseconds per
kilometer, which is negligible compared to typical disk latency of 5 to 10 milliseconds. The Brocade Extended
Fabrics feature enables full-bandwidth performance across distances spanning up to hundreds of kilometers. It
extends the distance ISLs can reach over an extended ber by providing enough buffer credits on each side of
the link to compensate for latency introduced by the extended distance.
Buffer Allocation
Buffer credits are a measure of frame counts and are not dependent on the data size (a 64 byte and a 2KB
frame both consume a single buffer). Standard 8-Gb transceivers support up to 150 meters. (Refer to Appendix
A for data rates and distances.) Users should consider the following parameters when allocating buffers for
long-distance links connected via dark ber or through a D/CWDM in a pass-thru mode:
1. Round-Trip Time (RTT)—in other words, the distance
2. Frame processing time
3. Frame transmission time
Some good general guidelines are:
•Number of credits = 6 + ((link speed Gb/s * Distance in KM) / frame size in KB)
•Example: 100 KM @2k frame size = 6 + ((8 Gb/s * 100) / 2) = 406
•Buffer model should be based on the average frame size
•If compression is used, number of buffer credits needed is 2x the number of credits without compression.