Specifications
DATA CENTER BEST PRACTICES
SAN Design and Best Practices 35 of 84
On the Brocade DCX 8510 with Gen 5 Fibre Channel platform, 4K buffers are available per ASIC to drive
16 Gbps line rate to 500 KM at 2KB frame size.
Brocade FOS v7.1 provides users additional control when conguring a port of an LD or LS link, allowing users
to specify the buffers required or the average frame size for a long-distance port. Using the frame size option,
the number of buffer credits required for a port is automatically calculated. These options give users additional
exibility to optimize performance on long-distance links.
In addition, Brocade FOS v7.1 provides users better insight into long-distance link trafc patterns by
displaying the average buffer usage and average frame size via CLI. Brocade FOS v7.1 also provides a new
CLI “portBufferCalc” that automatically calculates the number of buffers required per port given the distance,
speed, and frame size. The number of buffers calculated by this command can be used when conguring the
portCfgLongDistance command. If no options are specied, then the current port’s conguration is considered to
calculate the number of buffers required.
Note: The ClearLink D_Port mode can also be used to measure the cable distance to a granularity of 5 meters
between two 16 Gbps platforms; however, ports must be offline.
Fabric Interconnectivity over Fibre Channel at Longer Distances
SANs spanning data centers in different physical locations can be connected via dark ber connections
using Extended Fabrics, a Brocade FOS optionally licensed feature, with wave division multiplexing, such as:
Dense Wave Division Multiplexing (DWDM), Coarse Wave Division Multiplexing (CWDM), and Time Division
Multiplexing (TDM). This is similar to connecting switches in the data center with one exception: additional
buffers are allocated to E_Ports connecting over distance. The Extended Fabrics feature extends the distance
the ISLs can reach over an extended ber. This is accomplished by providing enough buffer credits on each side
of the link to compensate for latency introduced by the extended distance. Use the buffer credit calculation
above or the new CLI tools with Brocade FOS v7.1 to determine the number of buffers needed to support the
required performance.
Any of the rst 8 ports on the 16 Gbps port blade can be set to 10 Gbps FC for connecting to a 10 Gbps line
card D/CWDM without the need for a specialty line card. If connecting to DWDMs in a pass-thru mode where the
switch is providing all the buffering, a 16 Gbps line rate can be used for higher performance.
Recommendations include the following:
•Connect the cores of each fabric to the DWDM.
•If using trunks, use smaller and more trunks on separate port blades for redundancy and to provide more
paths. Determine the optimal number of trunk groups between each set of linked switches, depending on
trafc patterns and port availability.
FC over IP (FCIP)
Basic FCIP Architectures
Fibre Channel over IP (FCIP) links are most commonly used for Remote Data Replication (RDR) and remote tape
applications, for the purpose of Business Continuance via Disaster Recovery. Transporting data over signicant
distances beyond the reach of a threatening event will preserve the data such that an organization can recover
from that event. A device that transports FCIP is often called a channel extender.
RDR is typically storage array to array communications. The local array at the production site sends data
to the other array at the backup site. This can be done via native FC, if the backup site is within a practical
distance and there is DWDM or dark ber between the sites. However, more commonly what is available is a
cost-sensitive infrastructure for IP connectivity and not native FC connectivity. This works out well, because
the current Brocade technology for FCIP is very high speed and adds only a minute amount (about 35 µs) of
propagation delay, appropriate for not only asynchronous RDR and tape applications but also synchronous RDR
applications. Best practice deployment of FCIP channel extenders in RDR applications is to connect the FC
F_Ports on the channel extender directly to the FC N_Ports on the array, and not go through the production fabric