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Calling All Servers
Despite having invested millions of dollars in their SAN solutions, even large data centers often cannot afford to attach every server to shared storage. The barrier to entry for second-tier servers is simply cost. Even though overall administrative overhead can be reduced via SAN attachment, putting a $1500 Fibre Channel host bus adapter into a $3000 server is difficult to justify. In addition, the per-server attachment cost necessarily includes a corresponding per-port cost at the Fibre Channel switch or director.
So while mission-critical business applications are typically supported on high-end servers with redundant Fibre Channel HBAs to redundant SAN switches or directors, a company may still have less critical applications driven by hundreds (or in some cases, thousands) of low-end servers with direct-attached storage. These Wintel platforms running NT or Linux represent significant administrative overhead in terms of server code maintenance, over- and under-utilized storage capacity, and inefficient backup operations.
Integrating second-tier servers for large enterprises and accommodating economical server attachment for mid-range firms is now feasible with iSCSI technology. Since the applications on such platforms are typically less demanding, Gigabit Ethernet may be used to aggregate multiple servers over a single switched link.
Excluding the cost of the iSCSI switch port, the per-server attachment cost may be essentially zero if an iSCSI device driver (available for download from Microsoft and other vendors) is used on a standard Gigabit Ethernet or Fast Ethernet NIC (or range from $300 to $600 if a dedicated iSCSI NIC is used).
Depending on the fan-out ratio of iSCSI servers to iSCSI switch port, the cost of an iSCSI-to-Fibre Channel gateway can be amortized over tens or hundreds of servers. For low volume storage applications, this provides an economical means to leverage the benefits of SANs, including centralized storage management and streamlined SAN-based tape backup.
Although iSCSI is still not widely deployed, it is already putting pressure on Fibre Channel HBA pricing. To cover their options, most traditional HBA vendors have concurrent projects for both iSCSI adapters and new, lower-cost Fibre Channel HBAs. New HBAs in the $500 price range will lower the barrier to entry for conventional Fibre Channel SANs, although customers will still have the ability to mix higher performance HBAs for some servers with iSCSI attachment for others in the same SAN environment.
Multi-protocol Fibre Channel and IP SANs are enabling customers to apply the appropriate technology to service business applications based, not on technical considerations, but on the cost and availability criteria that align with business objectives.