This will not be the year that Serial Attached SCSI (SAS) makes gains on Serial Advanced Technology Attachment (SATA). SAS did not meet previous years' projected adoption rates and this year will be no different. Make informed storage decisions and forget the vendor hype.

Better Technology, Not a Better Value

Seagate Technology, Maxtor, and LSI Logic are among the vendors pushing SAS as a replacement for SATA. Adaptec is implementing a SAS-based SAN, but not all vendors are rushing to include SAS in their mid-sized solutions. Xiotech, for example, has indicated that there is currently no significant benefit to be gained from including SAS in its SME SAN solutions.

SAS and SATA Comparison
Device	Duty Cycle	Mean Time Before Failure (MTBF)	Seek Time (Average)
SAS (15,000 RPM)	24 hrs/day, 7 days/week	1,200,000 hours under enterprise workloads	3.6 ms
SATA (7200RPM)	8 hrs/day, 5 days/week	600,000 hours under desktop workloads	8.5 ms
Fibre Channel (15,000 RPM)	24 hrs/day, 7 days/week	1,400,000 hours under enterprise workloads	3.5 ms
SCSI (15,000 RPM)	24 hrs/day, 7 days/week	1,400,000 hours under enterprise workloads	3.5 ms

Traditionally, serial technology was good enough for keyboards and mice, but too slow for the high data transfer rates required for storage. Serial technology has improved to the point where it is a viable alternative to rapidly aging parallel interfaces (see chart above). SATA was introduced in 2002 with SAS following closely behind.

Today, SATA enjoys rapid adoption in the storage market, while SAS is still languishing. There are four main reasons why the SME market is not adopting SAS:

• SAS disks are really a large enterprise-class technology where the focus is on extremely high availability and reliability. Mean time before failure rates are in the millions of hours.
• Acquisition costs are still too high for the average SME purchaser to use SAS disks simply for nearline or backup storage.
• SATA drives are ideally suited for nearline storage and backup storage with a price point that significantly compensates for its lower reliability and availability.
• SATA drives are being widely adopted by SAN vendors like Dell/EMC, IBM, HP and others as part of their strategy to penetrate the mid-market. Because SATA provides significant savings compared to Fibre Channel, SCSI and SAS disks, SAN vendors can make their products more attractive to the SME market using SATA than they can with SAS.

Recommendations

1. Avoid vendors' push to migrate from SATA to SAS. Seagate and other disk manufacturers are already positioning SAS as the natural evolution of SATA for scalability and reliability. However, SMEs can safely and effectively manage their information using SATA disks in an appropriate RAID configuration. Only SMEs with mission-critical, highly available data requirements should consider purchasing SAS disks.
2. Compare apples to apples. SAS is an alternative to Fibre Channel, not to SATA. IT departments who have tier-one storage requirements and an immediate purchasing timeline should strongly consider SAS for their storage requirements because of SAS' high reliability, availability, and lower cost (compared to Fibre Channel).
3. Wait for SAS to replace Fibre Channel disks in SANs. IT decision makers planning to purchase a SAN in the next two years will see SAS drives become the disk of choice for tier-one SAN storage. Storage vendors will put SAS disks in their storage arrays instead of Fibre Channel since SAS has enterprise-grade reliability and availability, and is available at a lower cost than Fibre Channel disks. SMEs will benefit from this vendor strategy with lower TCO for enterprise-level resiliency.

Bottom Line

2005 is not the year of Serial Attached SCSI. SAS is not an appropriate fit for the majority of the SME market. It will not overtake SATA drives. IT decision makers in the SME market should only consider SAS if enterprise-level reliability and availability are key drivers.