Fibre Channel over IP
By WAYNE RICKARD
Network World, 06/12/00
Fibre Channel over IP leverages IP-based network services to connect storage-area network (SAN) islands over LANs, WANs or metropolitan-area networks, independent of link-level transport protocols. It solves a real user problem, is available today and has no ready substitutes. By contrast, SCSI over TCP/IP is still in the embryonic stages, faces significant technical obstacles and, for the near future, is a solution in search of a problem.
Fibre Channel over IP's main advantage is it needs no modifications to the storage subsystem or the server operating system. SCSI over TCP/IP, on the other hand, requires filter drivers so the server operating system can do IP-network-to-SAN emulation (for which I humbly propose the acronym INSANE). Unless we see Microsoft and other operating system vendors signing up for this mapping effort, practical implementations will be limited.
But why would anyone want SCSI over TCP/IP? The idea is positioned to connect servers (SCSI initiators) to disk drives or storage controllers (SCSI targets) using TCP/IP over Ethernet and WAN connections. A possible vision of the future has LAN-based storage protocols supplementing existing SAN and network-attached storage models - globally accessible net-attached disks, instant capacity scaling from LAN-connected storage service providers and raw data sharing over the Internet at close to wire speeds.
But do we really need SCSI over TCP/IP to do this? Storage over IP is here today. That's what file systems such as Network File System do.
Fibre Channel over IP solves real problems associated with building geographically remote storage subsystems. One of these problems is that Fibre Channel, which efficiently maps the SCSI storage protocol, typically supports links of 50 kilometers or less. In addition, distributed file protocols that can be bridged and routed over existing LANs and WANs need an extra remote server, can't be synchronized below the file level and must be independently implemented for each file system. Fibre Channel over IP solves these problems by supporting synchronized block I/O operations over long distances.
Further, the network interface at the Fibre Channel/LAN boundary can be tuned for performance by locking a path, using SONET, or assigning a dedicated wave division multiplexing channel. Security issues can be addressed by connecting over an IP-based VPN. While an end-to-end IP network transport cannot cost-effectively provide this level of service today, Fibre Channel over IP partitions the problem so the storage aspect is contained within the SAN, while the wide-area connectivity challenges (security, latency, bandwidth and reliability) are handled by mature WAN and IP technologies. Fibre Channel-to-LAN routers are ready now to drop into existing topologies and create real value for high-availability systems.
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Rickard is chief technical officer at Gadzoox, a SAN vendor in San Jose. He can be reached at wayne@gadzoox.com. |
