FIBRE CHANNEL and IP SAN INTEGRATION(3)

The maturity and mission-critical deployment of Fibre Channel (FC) in storage area networks (SANs) creates a unique class of multi-terabit networks with demanding throughput, latency, scalability, robustness, and availability requirements. This paper revie

For a fabric to be operational, there is a fabric initialization, involving all switches, directors, and devices. Initialization steps include parameter exchanges, Principal Switch selection, address assignment, path computation, and zone merge operations. As part of the path computation, directors and switches in a fabric run Fabric Shortest Path First (FSPF) routing protocol to build the forwarding data base. FSPF is a link state protocol that computes shortest path routes for frame forwarding. Within a FC fabric, there are name services and state change notification protocol services for resource discovery, configuration, and change management. FC zoning is an overlay network mechanism to limit the visibility and connectivity of servers to storage devices. A device can be in one or more zones, thereby enabling the sharing of servers (or clusters of servers) and storage resources. When an ISL changes state, all these protocols normally run, and when an end device comes up or goes down, name services and state change notification services run. These services consume more and more resources as the fabric size grows.2.2 Traffic Patterns in Fibre ChannelMost FC traffic uses the SCSI-FCP protocol [4] on top of FC Class 3 (unacknowledged datagram) service. SCSI-FCP is a request-response protocol that provides frame sequencing within transactions provided by lower-layer FC protocols. On frame loss or error, the protocol performs a transaction-level time out and retransmission. No retransmission of individual frames is supported. Time-out values are typically preconfigured and not based on actual round trip delay. The performance of SCSI-FCP is therefore sensitive to frame loss or frame level errors. Table 1 shows example read and write transactions and protocols frames. Transaction Protocol Direction Read Server to Storage Storage to Server Storage to Server Write Storage to Server Server to Storage Storage to Server Server to Storage Storage to Server Frame Type FCP_CMD (Read) FCP_XFER_RDY FCP_DATA (one or more) FCP_RSP FCP_CMD (Write) FCP_XFER_RDY FCP_DATA (one or more) FCP_RSP Typical Frame Length 68 Bytes 48 Bytes Up to 2084 Bytes 64 Bytes 68 Bytes 48 Bytes Up to 2084 Bytes 64 BytesTable 1 Example SCSI-FCP Read and Write Protocol Frames As bandwidth and delay product increases, it is critical to understand performance tuning and error recovery mechanisms. For configurations with long delay, it is important to consider the way data is moved (write or read). As shown in Table 1, the write transaction has one additional round trip delay more than the read transaction. Therefore, the read operation is faster when network delay is long.103

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