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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
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