New connections: SAS and iSCSI HBAs


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New server-to-storage host bus adapters offer significant performance gains, but there are some pitfalls to avoid.

Out with the old, in with the new: Serial-attached SCSI (SAS) and iSCSI host bus adapters (HBAs) are the new vanguard in server-to-storage connectivity. SAS HBAs are poised to replace parallel SCSI HBAs, while iSCSI HBAs offer companies the option to use an Ethernet storage network in lieu of a more costly Fibre Channel (FC) SAN for all of their servers.

Of course, SAS and iSCSI HBAs address different corporate storage connectivity needs. SAS HBAs help eliminate storage I/O throughput bottlenecks to internal or direct-attached storage (DAS) while expanding the number of storage devices a single server can address to more than 16,000. iSCSI HBAs open the door for organizations to connect high-performance servers to their Ethernet storage network.

A single SAS HBA card such as LSI Logic Corp.'s LSISAS3080X-R contains eight separate ports for I/O. Each port can operate at 3Gb/sec at half duplex and can concurrently communicate with both SAS and SATA hard drives. New iSCSI cards, such as Alacritech Inc.'s SES2100 and QLogic Corp.'s QLA4050C, improve TCP/IP offloading by separating the overhead from the server's CPU, which helps Ethernet networks meet the stringent I/O and throughput requirements of high-performance servers.

But despite these benefits, new iSCSI and SAS HBAs have their downsides. For example, SAS HBAs don't

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offer N_Port ID Virtualization (NPIV); as a result, a storage administrator must use one SAS HBA worldwide name per server. And if you need to reuse existing network-attached SCSI or FC storage devices with new iSCSI or SAS HBAs, you'll need a bridge or router for the SAS or iSCSI HBA to communicate with those legacy storage devices.

This was first published in April 2007

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