HP A7533A - Brocade 4Gb SAN Switch Base, Administrator'S Manual

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Fabric OS 6.2 administrator guide 471
4. The PI continues to stage data received from the initiator, respond locally to a Transfer Ready, and send
the data to the target device until the target device sends a Response (FCP_RSP).
Figure 83 How FC Fastwrite works
FC Fastwrite can improve write performance. Read performance is unaffected. The gains seen from
enabling FC Fastwrite depend on several factors, including the following:
• The size of I/O versus Transfer Ready (Tx_RDY). In general, the more times a target device sends a
Tx_RDY, the greater the performance gain.
• The number of outstanding I/Os, both read and write, link speed, and link congestion. FC Fastwrite
may not result in significant improvement if these factors suggest that the write data is delayed because
it is sharing bandwidth.
• Target response latency—If the target is slow in responding to the write command, the data must be
held by the remote switch.
FC Fastwrite flow configuration requirements
Because FC Fastwrite is enabled on both initiator and target ports there is a possibility that either initiator
or target ports may have flows with other devices that do not support FC Fastwrite. Therefore an FC
Fastwrite-specific zone configuration is used to filter FC Fastwrite flows.
Hardware considerations for FC Fastwrite
FC Fastwrite is implemented in a hardware configuration consisting of two HP StorageWorks 400
Multi-Protocol Router, or two HP StorageWorks 4/256 SAN Director, or two HP StorageWorks DC SAN
Backbone Director or HP StorageWorks DC04 SAN Director Switch enterprise-class platforms with B-Series
Multi-Protocol Router Blades connected by Fibre Channel ISLs. Consider the following hardware
characteristics and requirements when planning to implement FC Fastwrite:
• FC ports on both the HP StorageWorks 400 Multi-Protocol Router and the B-Series Multi-Protocol Router
Blade are organized into two groups. Ports 0-7 form one group, and ports 8-15 form the other. A
maximum of four ports in each group may be configured as FC Fastwrite.
• The maximum bandwidth available for FC Fastwrite is 4 Gb/s per group. This bandwidth is shared by
all write flows.
• Host initiators and target devices must be directly connected to the HP StorageWorks 400
Multi-Protocol Router or B-Series Multi-Protocol Router Blade on their respective ends of the ISL. FC
Fastwrite must be configured and enabled for the ports on both ends of the flow. Mismatch of the
configuration results in I/O failure.
Configuring and enabling FC Fastwrite
The FC-FC Routing Service provides Fibre Channel routing between two or more fabrics without merging
those fabrics. The FC-FC Routing Service can be simultaneously used as a Fibre Channel router and for
SAN extension over wide area networks (WANs) using FCIP.