12Gbs SAS, What Does it Mean for SATA?

With current market availability of 12 Gigabit SAS, and wide distribution expected by the end of 2015, many wonder what that will mean for SATA.  At the time of this writing there are no plans to bring SATA III from 6Gbs to 12Gbs. There are many differences between SAS and SATA that often go overlooked and within the hard drive world especially because the price differential for the raw drive can be less than $50.  SAS leverages the SCSI command set which offers significant robustness for error handling, signal distance, parallel commands, and more when compared to SATA. The advent of 12Gbs SAS will enable storage arrays to take great advantage of the SCSI command set increasing throughput way past the 550Mbs range we see out of a typical SAS drive today.

Interestingly the improvement to the SAS bandwidth actually helps SATA drives. SATA is physically plug-compatible with SAS and while each individual drive is not going to go past 6Gbs the backplane and the expanders that communicate with these drives will support more bandwidth. Architects try to design active archive systems to be as dense as possible in an effort to reduce power space and cooling costs. A 12Gbs SAS backplane could potentially provide a significant advantage to these systems.

SAS will receive accelerated selection for performance use cases for both IOPS and throughput.  SSDs with 12Gbs SAS will be able to outperform SATA because of the bandwidth and the support for greater queue depth. ATA only supports a queue depth up to 32 while SAS supports 65,536 but is typically only implemented up to 128 with 6Gbs SAS drives. The performance gap between SAS and SATA will become very significant in the days to come because of the fundamental improvements to the SAS-3, 4th generation SAS standard.

My prediction is that SATA will continue to be the disk standard of choice for large archive and performance neutral requirements because the price difference is negligible between 6Gbs SAS and SATA. However, it seems likely that vendors will push for a larger price disparity between 12Gbs SAS and 6Gbs SATA. 12Gb SAS, both HDD and SSD, will be the new norm for primary storage and situations when performance matters because of its superior IOPS, throughput, and data integrity.

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