9.3 Metropolitan- and Wide-Area Storage Network Products

9.3 Metropolitan- and Wide-Area Storage Network Products

As shown in the previous section, IP storage can be used for metropolitan- and wide-area networking, regardless of the type of SAN used. Fibre Channel currently is, by far, the most common SAN protocol, but the IP storage protocols, iSCSI and iFCP, now have begun to move into the SAN itself.

Ultimately, pure IP storage networks will use iSCSI in every end system, but with several million Fibre Channel end systems already in use and iSCSI end systems just emerging, the conversion to pure IP could take many years . Meanwhile, two transition protocols have been developed (FCIP and iFCP) to enable Fibre Channel SANs and end systems to communicate over standard IP networks.

FCIP ( Fibre Channel over Internetworking Protocol) was developed as a simple tunneling protocol for interconnecting Fibre Channel SANs over IP networks. iFCP (Internet Fibre Channel Protocol) also was designed for linking Fibre Channel SANs over IP, but has advanced features that offer better scalability and manageability, and it can be used for building IP SANs within the data center. Figure 9-7 shows a summary of the IP storage protocol recommendations.

Figure 9-7. IP storage protocol recommendations for SANs, metropolitan-, and wide-area connections.

The iSCSI and iFCP protocols support data center SANs as well as metropolitan- and wide-area IP storage networking. In IP SAN applications, the core of the SAN is native IP and Ethernet ”the same protocols used in MANs and WANs ”so no additional conversion is needed to connect an IP SAN to the backbone network. A single iSCSI or iFCP product can be used for both the SAN and the MAN and WAN access, as shown in Figure 9-8.

Figure 9-8. Native IP SANs can be interconnected across metropolitan and wide areas with no additional conversion equipment.

Within the data center, IP SANs can be expanded easily, using off-the-shelf Gigabit Ethernet switches, which now support well over 200 wire-speed ports. As shown in Figure 9-9, native IP (iSCSI) end systems can be connected directly to the Gigabit Ethernet core switches, and Fibre Channel end systems can be linked to the core switches using standard multiprotocol storage switches that support IP, iSCSI, and iFCP.

Figure 9-9. IP SANs can be expanded easily, using standard Gigabit Ethernet core switches.

It seems likely that at least a one-port FCIP or iFCP gateway could be built into an interface card for a Fibre Channel switch, and some Fibre Channel switch vendors have announced that they are working on that capability. That would offer the advantage of eliminating the external Fibre Channel-to-IP conversion switch. However, the SAN itself then would remain as a conventional Fibre Channel switch fabric rather than being a native IP SAN, so another (iSCSI) interface card would have to be developed for the Fibre Channel switch to support native iSCSI end systems.

With IP end systems, a Fibre Channel core, and an IP MAN or WAN, it would be necessary to convert iSCSI into Fibre Channel and then back again to IP (FCIP or iFCP) for connecting to MANs and WANs. Managing such a network could be a challenge, and there may be some danger that the iSCSI control frames would be lost during the multiple protocol conversions as they travel from end to end. Therefore, it's probably simpler and safer to use an IP core if the SAN contains iSCSI end systems.