Peaceful Coexistence Of Fibre Channel And IP Storage.

Fibre Channel and IP Storage SANs will coexist because they have different strengths and are suited for different applications and markets. Fibre Channel will continue to be a good SAN solution in enterprise data centers. IP Storage, with a lower projected total cost of ownership (TCO), will become widely adopted in small and midsized companies and data centers. IP storage protocols now being standardized will also be used to connect Fibre Channel SANs to each other.

Fibre Channel

Fibre Channel's strengths (Figure 1) include high performance with relatively low latency, and the ability to connect across campus distances. Also, Fibre Channel products are generally available today from a wide range of storage and interconnect vendors. Users who have already made an investment in Fibre Channel technology and skills have already paid much of the "cost of entry." For those who haven't, customers have the benefit of lessons learned by the earlier adopters.

Fibre Channel was developed specifically to attach servers to storage as efficiently as possible in a variety of topologies. Fibre Channel specifications address the need for scalability, availability, and distance. FC-AL (Fibre Channel-Arbitrated Loop) configurations incorporate redundancy and switched FC fabric provides redundancy, alternate path routing, and zoning.

With 1 Gbps Fibre Channel products currently available, peak full-duplex throughput of 200MB/sec is achievable. With the new 2Gb products now appearing, it's possible to double that throughput. Focus is also beginning to shift to 10Gbps.

Support for Fibre Channel has been built into most storage management applications, and a new class of applications--SAN management--has emerged.

Typically, for end-user adoption of any new technology, a wide variety of vendors must bring products to market to provide function, feature, and price competitiveness, allowing users choices and the opportunity to switch vendors. Fibre Channel has achieved the necessary critical mass of alternative products and technology sources.

Given the strengths of Fibre Channel, it is an appropriate choice for large enterpriselevel companies for applications that require the highest performance, and whose budget allows for a dedicated infrastructure and skills.

Because of the distance limitations inherent in a Fibre Channel SAN, suitable applications are those where storage subsystems are grouped within a data center or nearby at campus-type distances.

Fibre Channel SANs will continue to be deployed in large enterprise-level data centers for the next few years, but widespread deployment outside of these large installations is unlikely to occur.

Complete end-to-end Fibre Channel solutions such as LAN-free backup are starting to emerge in the distribution channels. This will provide an opportunity for Fibre Channel to move into markets that do not yet have any Fibre Channel products. These customers will need to assess the extent and timing of their need for SAN technology, and whether or not to wait for IP Storage SAN solutions.

IP storage

IP Storage (Figure 2) can be used either to implement SANs or to connect geographically dispersed SANs together thereby enhancing and extending the life of FC SANs. IP Storage can be viewed as an additional market enabler of Fibre Channel SANs. However, the greatest potential for IP Storage is as an alternative to Fibre Channel to implement SANs using the iSCSI protocol now being standardized.

iSCSI is the Internet Engineering Task Force (IETF) specification that defines how SCSI and Ethernet work together to perform SCSI data transfers across TCP/IP networks. It allows today's block storage SCSI commands to be carried by the standard TCP/IP protocols over Ethernet. The SCSI and Ethernet standards are each mature, stable, ubiquitous, and interoperable. These qualities provide a solid foundation on which to build a SAN fabric.

For the next two or three years, until broad deployment of 10Gb Ethernet, Fibre Channel will continue to offer higher peak performance and lower latency than IP Storage. However, many applications that work well with 1Gb Fibre Channel today will work equally well on 1Gb Ethernet.

With the increasing popularity of 1Gbit Ethernet, building iSCSI SANs will become increasingly attractive to small and mid-sized organizations where the high cost and complexity of Fibre Channel is not an option. iSCSI maintains all of the manageability, cost effectiveness, versatility, and compatibility that has made Ethernet the dominant networking technology today. Also, Network Attached Storage (NAS) products and filers are becoming increasingly common, so the notion of attaching storage boxes to Ethernet networks has already been embraced by customers of all sizes.

A vast array of Ethernet equipment and tools are available from many vendors today, and they are fully interoperable. 1Gbps Ethernet equipment supports the installed base of earlier (10Mbps, 100Mbps) Ethernet equipment. A user buying Ethernet infrastructure products can be confident they will be compatible and interoperable with equipment from other suppliers. The same cannot be said for Fibre Channel products, however.

Gigabit Ethernet products that can operate over existing Category 5 cabling infrastructure are widely available from multiple vendors today, so companies that want to move to Gigabit Ethernet for communications or storage net working do not have to install new copper cable or fiber-optic infrastructure. An IT manager planning to build a storage network and has not yet installed a Fibre Channel infrastructure must pay to install and manage that new infrastructure in addition to the existing Ethernet one.

The roadmap for Ethernet is well defined through 100Gbps, and hundreds of millions of R&D dollars are being invested annually to bring interoperable 10Gbps Ethernet technology and products to market. This will translate into more 10Gbps Ethernet products from more suppliers sooner than will be possible with 10Gbps Fibre Channel. The cost and price leverage resulting from higher volumes can be seen in the price differences between 1Gbps Ethernet and 1Gbps Fibre Channel switches.

Almost every operating system and application today has robust SCSI device drivers and SCSI device support features. The SCSI command protocol is also used in Fibre Channel to avoid the need to change applications and device drivers supporting the massive installed-base of SCSI storage devices.

Although iSCSI can be implemented in the host above the operating system's TCP/IP stack and use off-the-shelf NICs (network interface cards), realizing the full performance potential of iSCSI requires host bus adapters (HBAs) that offload TCP/IP processing from the host CPU. Adaptec has already announced a family of such HBAs. The first Adaptec offload HBA, the AEA-7110C, is being sampled to OEMs now and will ship by the end of this year. In the future as the iSCSI protocol standard is finalized, more highly integrated "accelerated protocol" chips will emerge that will allow even lower-cost implementations to be available.

Fibre Channel is a good SAN technology for large IT environments where cost and complexity are not the most important issue, and is available today. For the midsize market and small companies, iSCSI SANs over Ethernet are an attractive alternative. Ethernet is pervasive and well understood by IT personnel, and it provides the advantages of a single network infrastructure for storage and communications. For the next several years both types of SANs will become widely deployed and coexist comfortably together.

Brent Ross is the director of product marketing for the Storage Networking Group at Adaptec, Inc. (Milpitas, CA).