Although the steady penetration of Storage Area Networks (SANs) into the market continues, it has so far been limited largely to top-tier companies and institutions. By generous estimates, less than 20 percent of the potential market for shared-storage solutions has actually adopted SANs. This low percentage is due in part to high acquisition costs of Fibre Channel storage and to the complexity and management concerns associated with SAN technology. Although small and midsized businesses can also benefit from the storage consolidation, tape backup, and high-availability applications that SANs enable, making the transition from Direct Attached Storage (DAS) to shared storage with limited budget, staff, and SAN expertise is often difficult. However, new SAN products are facilitating this change by reducing acquisition costs and maximizing use of existing corporate network infrastructures.
The Internet SCSI (iSCSI) host adapters, IP storage switches, and iSCSI-to-SCSI bridge products now available are changing the composition of SANs. Homogeneous Fibre Channel fabrics must now accommodate IP networking, both for classic SAN extension applications such as disaster recovery and for heterogeneous mixtures of iSCSI and Fibre Channel end devices. With the introduction of native iSCSI interfaces on storage arrays in early 2003, the multiprotocol composition of SANs will shift even more dramatically toward IP. And as the IP content increases, the market penetration of SANs will also increase. Companies that couldn't previously assume the burden of cost and complexity of Fibre Channel fabrics now have options for implementing SANs that conform to the rest of their data communications networks.
Large networking vendors, such as Intel, are driving down the cost of iSCSI host adapters (i.e., storage accelerators or storage NICs). Justifying the installation of a $1200 Fibre Channel host bus adapter (HBA) in a $2000 server was difficult, but justifying a $600 iSCSI card that accomplishes the same task is easier, and plugging the iSCSI adapter into a standard Gigabit Ethernet switch port instead of a dedicated Fibre Channel switch cuts the per-port cost roughly in half. iSCSI host attachment eliminates other costs as well, such as the cost of special equipment otherwise needed to extend SAN connectivity over a distance. Standard IP switches and routers provide the SAN transport regardless of physical location.
Systems still require IP storage switches to bring Fibre Channel storage and end devices into an IP SAN but currently don't offer a significant cost savings over Fibre Channel fabric switches. Financially, the benefit of IP storage switches is primarily in cost avoidance. For example, IP storage switches enable both Fibre Channel and iSCSI hosts to access Fibre Channel storage targets over traditional IP networks. This solution avoids the cost of implementing and managing a Fibre Channel fabric, with its complexity and requirement for special diagnostic tools and expertise.
iSCSI-to-SCSI bridges open up the mass IT market to SAN solutions. These products enable customers to bring their legacy SCSI disk arrays and tape devices into a shared IP SAN. Unlike the previous generation of Fibre Channel-to-SCSI bridges, connectivity to the SAN no longer mandates expensive Fibre Channel switches or Fibre Channel hosts. Instead, SCSI storage can be bridged to a common IP network infrastructure and shared by iSCSI-attached servers. As an add-on value, some vendors are integrating storage-virtualization capability into iSCSI-to-SCSI bridges so that even small and midsized businesses can enjoy the benefits of storage pooling. Collectively, iSCSI adapters, IP storage switches, and iSCSI-to-SCSI storage concentrators are bringing shared storage solutions to a broad spectrum of customers.