SAS challenges Fibre Channel drives


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In their 3 Gbps incarnation, SAS drives have proved popular in low-end and nearline data storage systems, but at 6 Gbps, SAS-2 poses a serious threat to Fibre Channel interface drives.

Since its introduction in 2004, serial-attached SCSI (SAS) has become the prevailing data storage interface in servers and is on a trajectory to become the same for external storage systems. Those systems are still dominated by Fibre Channel (FC) and serial ATA (SATA) disk drives, but next-generation SAS-2 components, available since early 2009, are hastening this transition.

With 6 Gbps transfer rates and enhancements that neutralize some of the shortcomings of SAS 1.1, SAS-2 has overtaken FC as the most advanced and fastest disk interface. Because FC drives with their 4 Gbps transfer rate and 3.5-inch form factor have reached the end of the road, it's only a question of time as to when SAS will emerge as the drive interface of choice for high-end storage systems and servers. Thanks to its prevalence in servers today, SAS -- mostly 3 Gbps SAS -- already owns approximately 40% of the multiuser disk interface market, trailing SATA's 41.7% share and outpacing the 16% market share of FC-AL/4 Gbps, according to recent analysis by Stamford, Conn.-based Gartner Inc. "SAS will account for 57% and SATA for 43% of the total multiuser HDD [hard disk drive] market by 2013," predicted John Monroe, a Gartner research vice president, who pegged the extinction of FC drives

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to the year 2013.

The impact of SAS on FC and SATA drives

Despite some disagreement on timing, most data storage analysts agree that the days of FC as a disk interface are numbered. Fibre Channel disks were never able to extend beyond high-end servers and storage arrays and, as result, costs remained high (e.g., a SAS host bus adapter [HBA] costs approximately one-third the price of a comparable FC HBA). Moreover, users have been coping with disparate disk interfaces -- FC for high performance and SATA for large-capacity storage -- requiring conversion chips for the two to coexist in a single storage system. Conversely, SAS and SATA can be supported by a single chip, reducing interface costs, complexity and power requirements. "Enterprise-class SAS drives are on par with high-end FC drives, except SAS has a smaller cooling and power footprint, and enables a single back-end interconnect technology for both SAS and SATA," said Tony Palmer, senior engineer and analyst, ESG Lab at the Milford, Mass.-based Enterprise Strategy Group (ESG).

This was first published in January 2010

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