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iSCSI gateways perform protocol translation from iSCSI to FC and vice versa. They typically come with at least two FC ports to connect to back-end FC storage and a minimum of two 1Gb Ethernet ports to provide IP connectivity to servers. iSCSI gateways present FC LUNs as iSCSI targets, making FC storage accessible over IP and obviating the need for FC HBAs in servers. Examples of these gateways include Brocade Communications Systems Inc.'s iSCSI Gateway, Cisco Systems Inc.'s MDS 9216i, Emulex Corp.'s 725/735 iSCSI Storage Routers and QLogic Corp.'s SANbox 6140 Intelligent Storage Router.
Storage provisioning in SANs with iSCSI gateways requires two steps. FC storage admins provision LUNs to the iSCSI gateway, and then iSCSI access to FC LUNs is restricted on the iSCSI gateway to defined IP addresses, initiator-target names or via CHAP credentials. Once this is accomplished and the iSCSI initiators have been properly configured on iSCSI clients, they can see assigned storage as local disk drives.
|Lessons from the field|
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The main benefit of iSCSI gateways is their simplicity and unobtrusiveness when added to an existing FC SAN. They don't require architectural changes on the FC network and allow servers to access FC storage by simply configuring the iSCSI initiator software. But iSCSI gateways aren't cheap--street prices start at approximately $10,000 for a single iSCSI gateway appliance. With FC HBAs costing at least $400 for Windows and Linux systems, the cost-benefit analysis is straightforward: An iSCSI gateway can only be justified if a relatively large number of servers use it. For a small number of servers, it's more economical to add FC HBAs to servers to directly connect to the FC SAN. "You need about 100 servers before you see a real price-performance benefit of iSCSI gateways," says Mario Blandini, Brocade's director of product marketing.
This was first published in February 2007