Shared Storage for the Masses

The steady penetration of storage area networks (SANs) into the market continues, but so far has been largely limited to the top tier companies and institutions. By generous estimates, less than 20% of the potential market for shared storage solutions has actually adopted SANs. This is due in part to higher acquisition costs of Fibre Channel storage and in part to the complexity and management issues associated with SAN technology. Although small and medium businesses (SMBs) can also benefit from the storage consolidation, tape backup and high availability applications that SANs enable, it is often difficult to make the transition from direct-attached to shared storage with limited budget, staff and SAN expertise. New SAN products, however, are facilitating this change by reducing acquisition costs and maximizing use of existing corporate network infrastructures.

The iSCSI host adapters, IP storage switches and iSCSI-to-SCSI bridge products now available in the market are changing the complexion 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 multi-protocol composition of SANs will shift even more dramatically towards IP. As the IP content increases, however, the market penetration of SANs will also increase. Companies that could not 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.

Thanks to large networking vendors such as Intel, the cost of iSCSI host adapters (a.k.a. storage accelerators or storage NICs) is being driven into a more affordable price range. While it was difficult to justify installing a $1200 Fibre Channel Host Bus Adapter in a $2000 server, it is more reasonable to install a $600 iSCSI card that accomplishes the same task. The iSCSI adapter, in turn, may be plugged into a standard Gigabit Ethernet switch port instead of a dedicated Fibre Channel switch, at roughly half the per-port cost. iSCSI host attachment eliminates other costs as well, such as special equipment to extend SAN connectivity over distance. Standard IP switches and routers now provide the SAN transport, regardless of physical location.

IP storage switches are still required to bring Fibre Channel storage and end devices into an IP SAN, but currently do not offer a significant cost savings over Fibre Channel fabric switches. The cost benefit for these devices is primarily in cost avoidance. IP storage switches, for example, enable both Fibre Channel and iSCSI hosts to access Fibre Channel storage targets over traditional IP networks. This solution avoids the costs of implementing and managing a Fibre Channel fabric, with its associated 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 more expensive Fibre Channel switches or Fibre Channel hosts. Instead, SCSI storage can be bridged into a common IP network infrastructure and shared by iSCSI-attached servers. As a value-add, some vendors are integrating storage virtualization capability into iSCSI-to-SCSI bridges so that even small and medium 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.