Look toward a strategic storage network: high-level issues remain to be resolved. (Special focus: storage technologies).

Companies growing data at an exponential rate must scale storage capacity in a more secure, manageable and cost-efficient manner. To control associated management costs, the storage networking model--of which network-attached storage and storage area networks (SANs) are part, and which is replacing traditional server-attached storage--responded. Now, storage capacity can be more effectively utilized, and the storage environment simplified.

Potential benefits include economies of centralized storage management/administration, opportunities for enhanced intelligence in data presentation/delivery, and creation of a policy-based storage provisioning capability, adaptable to changing application/business requirements.

The InterNational Committee for Information Technology Standards developed the Fibre Channel storage interconnect, which redressed some limitations associated with the small computer systems interface (SCSI) bus. Using Fibre Channel, storage devices could be spaced further away from servers, and more devices supported on a single host bus adapter.

An important step was defining how the SCSI protocol would operate over Fibre Channel and would provide storage access transparency to the application, whether storage was connected via SCSI or Fibre Channel. Fibre Channel vendors and storage network integrators embraced this concept, resulting in a number of storage network solutions that addressed select storage infrastructure requirements.

Collaborating storage and networking vendors significantly enhanced storage networking using TCP/IP, the popular and readily available existing networking protocol. The Internet Engineering Task Force (IETF) has focused on IP storage networking through the iSCSI (Internet SCSI), which is developing standards for running the SCSI protocol over TCP/IP, and through two subgroups developing standards for encapsulating Fibre Channel frames for transmission over TCP/IP. One subgroup is developing a point-to-multipoint connectivity standard called Fibre Channel over IP (FCIP), the other, a routable method of encapsulating Fibre Channel frames called Internet Fibre Channel protocol (iFCP).

The iSCSI initiative treats the TCP/IP network as a reliable transport similar to Fibre Channel, but with the scalability, security and ease of management inherent to TCP/IP. SCSI commands and data are encapsulated onto the TCP/IP network via a host bus adapter configured like a network interface card currently used to connect systems to a network.

Ideally, any standard network link, including Ethernet, can physically interconnect devices and systems. Any IP switch can switch storage-related traffic between devices. Thus, an enterprise storage network currently can be constructed using familiar techniques and equipment.

By contrast, discussions of Fibre Channel over IP revolve around efforts to utilize the TCP/IP network to transport Fibre Channel data streams between SAN "islands" or between Fibre Channel host bus adapters and Fibre Channel storage devices. In some designs, a bridge/router provides the necessary connectivity to the TCP/IP network at both ends. This approach has been described as tunneling Fibre Channel across the IP network.

Both have promise and solve different problems. iSCSI over TCP/IP, strategically, will provide the capability to leverage any existing LAN technology and knowledge base to field storage networks quickly and efficiently. A storage network usually will be a private network and will not burden the existing data network, iSCSI will also permit SANs to be managed and secured using standardized protocols already developed, tested and proven within the IETF as components of the TCP/IP networking suite. Fibre Channel over IP, used to interconnect first-generation Fibre Channel SAN "islands," can preserve an existing infrastructure investment in Fibre Channel.

Both Fibre Channel and iSCSI over TCP/IP have enormous potential to provide the foundation for a networked storage infrastructure. Many end-users are deploying iSCSI to link large numbers of servers to storage pools that are Fibre Channel based. Storage routers can convert iSCSI to FCP and provide log-in/logical-unit-numbers mapping to make storage pools secure.

Challenging issues remain: how storage networks will interact with servers, deliver secure virtual volumes that are dynamically resized, provide always-on storage and enable support for heterogeneous servers and storage devices. By comparison, fixing the plumbing of storage networks is mundane.

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Jurgens is a business development manager at Cisco's storage router business unit, Maple Grove, MN.