Bringing SANs to the Masses Page 2


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More Affordable Shared Storage via iSCSI

Although storage assets represent the lion's share of a SAN investment, cost reductions in server connectivity and the storage network infrastructure are also improving the total cost of ownership equation for SANs. iSCSI and IP storage switching are making shared storage more affordable by enabling customers to use more of their existing IP networks and staff to support storage applications. iSCSI is already available at no cost as a device driver that can be loaded on traditional, low cost Ethernet and Gigabit Ethernet network cards. Specialized iSCSI adapter cards with TCP off-load chips are currently available at less than half the cost of comparable Fibre Channel host bus adapters. Although iSCSI is currently unproven as a technology for higher end data center applications, it can sufficiently support normal storage applications such as block-based tape backup and moderate performance departmental data applications.

In addition to lower cost adapter cards, iSCSI offers further savings by leveraging conventional Ethernet and Gigabit Ethernet switches for the SAN core. Instead of tethering servers to dedicated and more expensive Fibre Channel fabric switches, servers can be deployed anywhere within an IP-routed network at less than half the cost per switch port. To benefit from this economy, however, the customer must understand their actual bandwidth and application requirements to avoid over-subscribing storage ports and degrading performance.

At the low end of the market, iSCSI-to-SCSI bridge products offer an affordable means to enjoy the benefits of shared storage at minimal cost. iSCSI-to-SCSI bridges enable customers to access their existing direct-attached SCSI storage devices from iSCSI-enabled servers. Some products in this class also provide rudimentary storage pooling capability as a means of simplifying storage allocation and administration. If the customer's SCSI devices are already in place, and if software iSCSI device drivers are used on the hosts, the entry point to a SAN is essentially free once the iSCSI-to-SCSI bridge is put in place.

iSCSI will not displace traditional Fibre Channel in the foreseeable future, but it does expand the market for SAN solutions in general. SAN storage arrays, for example, are still Fibre Channel-attached and require IP storage switches to provide protocol conversion between iSCSI and Fibre Channel. But since iSCSI dramatically reduces the cost of attaching additional servers, it facilitates bringing larger populations of devices into the SAN. Still, for high performance applications, Fibre Channel host bus adapters will remain the product of choice.


The combination of modular storage, more economical disk drives, and iSCSI host connectivity makes SAN solutions more economically attractive for departmental and small business applications. Customers who previously could not justify the expense of a SAN for their less critical applications can now gain the benefits of SAN technology on a more modest budget. As already demonstrated by Ethernet and IP technology, pervasive deployment and cost reduction create a mutually reinforcing cycle that benefits both customers and the industry.

Tom Clark
Director of Technical Marketing, Nishan Systems
Author: Designing Storage Area Networks Second Edition (2003) (available at Amazon.com), IP SANs (2002) (also available at Amazon.com)

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