2.7 IP SAN Protocols

Throughout 2001 and 2002, the IP storage industry spent considerable time addressing the underlying protocols for IP storage. The SNIA IP Storage Forum (www.ipstorage.org), an industry group within the SNIA, provides valuable informational and educational materials on IP storage, including the protocols. The standards ratification process for IP storage is conducted by the IETF (www.ietf.org), the same organization that has standardized and ratified the protocols relating to IP and the Internet.

The three IP storage transport protocols currently under consideration by the IETF reflect unique strategies for block data over TCP/IP networks. They are iSCSI, iFCP, and FCIP, shown in Figure 2-18.

Figure 2-18. Protocol options for IP storage.

The technologies fall into two categories:

• The Fibre Channel over IP (FCIP) protocol is a Fibre Channel perpetuation strategy for linking Fibre Channel fabrics over distance. FCIP has minimal IP content facilities, since its aim is not to replace Fibre Channel with IP but simply to facilitate further deployments of Fibre Channel fabrics via IP tunneling.

• The Internet Fibre Channel Protocol (iFCP) and Internet SCSI (iSCSI) protocols, by contrast, are IP strategies for supplementing or replacing Fibre Channel fabrics with Gigabit Ethernet and IP infrastructures .

This basic distinction between Fibre Channel and IP strategies reveals fundamental assumptions about market directions and the solutions that customers may deem most viable . As a Fibre Channel strategy, FCIP assumes that current Fibre Channel fabrics are appropriate for data center SANs and that IP is only required to accommodate distances that exceed the capabilities of native Fibre Channel. Both iFCP and iSCSI make the opposite assumption. iFCP and iSCSI address the limitations of Fibre Channel fabrics for both data center and remote SAN connectivity. Since iFCP and iSCSI are native IP solutions for storage end devices, Fibre Channel fabrics are no longer required. The iFCP protocol is designed to support Fibre Channel end devices, and it substitutes an IP infrastructure in place of Fibre Channel. It also has the capability to incorporate existing Fibre Channel hubs and switches, if present. The iSCSI protocol ultimately replaces both storage end devices and the storage transport with IP technology. Thus while FCIP represents Fibre Channel perpetuation, iFCP represents migration transition from Fibre Channel to IP SANs, and iSCSI represents the ultimate goal of homogeneous IP storage networking.

As native IP storage protocols, iFCP and iSCSI are complementary. The iFCP protocol addresses the current SAN market in which both server platforms and storage devices use Fibre Channel interfaces. The current HBAs, Fibre Channel RAIDs, JBODs, and tape subsystems enjoy a much higher degree of interoperability and stability than Fibre Channel fabric switches. The iFCP protocol enables these Fibre Channel end systems to be joined over an IP network, both for data center applications and for wide area requirements. It offers customers the option of using familiar and more manageable Gigabit Ethernet switches and IP routers to build enterprise SANs. This allows SANs to be more easily incorporated into mainstream data communications implementation and management. Aside from overcoming the complexity and interoperability issues of Fibre Channel fabrics, iFCP enables customers to start building IP SANs today. By attaching current Fibre Channel end systems to IP networks, IP storage switches supporting iFCP (and iSCSI) create a foundation on which data center, metropolitan, and wide area storage applications can be built over time. This foundation is the common architecture that will support iSCSI end devices as well.

While iFCP provides the migration transition path from present to future SANs, the iSCSI protocol is the enabling technology for homogeneous IP SANs. The development of iSCSI storage NICs and iSCSI interfaces on storage and tape devices will allow customers to treat storage as just additional nodes on the network and to fully utilize the functionality of IP networks for storage. As with iFCP, leveraging IP and Gigabit Ethernet technology for the SAN fabric allows iSCSI to implement advanced services for storage, such as quality of service levels and encryption of storage data. As iSCSI products based on Gigabit and 10 Gigabit Ethernet come to market, customers will be able to synchronize their requirements for network messaging and storage backbones, and deploy a common network infrastructure for a variety of application needs.

It is worth noting that iSCSI affords customers the option of building native iSCSI solutions without relying on other technologies. Customers can build iSCSI SANs or use iSCSI devices alongside NAS storage.

While Fibre Channel-based storage currently represents the upper layer of the enterprise market, sustained adoption is a market reality. Customer awareness for best of breed Fibre Channel storage deployment options combined with best of breed IP and Ethernet storage networking will drive the adoption of native iSCSI. Customers will always gravitate to solutions that are more familiar, more manageable, and more easily supported. Use of iFCP in IP storage switches or gateways allows customers to minimize their Fibre Channel exposure and maximize benefits of mainstream IP networking. Products based on iSCSI will take this transition a step further by creating iSCSI SANs connected to IP networks. In combination, iFCP and iSCSI solutions thus take customers from where they are today to where they need to be tomorrow.