Conclusion
SAS 6 Gb/s represents a logical and desireable evolution of the SAS architecture. It simplifies management of complex storage deployments, while speeding up individual links from 3 Gb/s to 6 Gb/s.
Performance will probably be the most important reason for people to adopt SAS 2.0, although we have to underline that the second generation really has matured. Zoning and external cabling have now been standardized, removing the complexities and confusion tied to proprietary solutions. SAS 6 Gb/s is now a true competitor to Fibre Channel solutions, even in advanced, mid-range enterprise scenarios.
Where 6 Gb/s Doesn’t Make a Difference
Performance advantages make great headlines, but be aware that this generation of SAS only delivers a benefit in storage environments based on expanders and appliances, where you have a plethora of drives being accessed through relatively narrow data pathways. Even the fastest new SAS 6 Gb/s drive, Seagate’s Cheetah 15K.7, is still limited to 200 MB/s maximum throughput when operated in one-drive configurations.
This can already be handled by SAS 1.1 at 3 Gb/s (300 MB/s). We’ll have to wait at least two more hard drive generations to see an individual drive saturate 3 Gb/s bandwidth. So, there’s not much benefit in focusing on getting 6 Gb/s SAS into systems running only small RAID arrays or individual hard drives. There simply won’t be a noticeable benefit.
The True 6 Gb/s SAS Value
However, things change rapidly once wide ports are used to talk to SAS storage appliances. Without wide ports, the aggregate bandwidth of so many drives can swamp a conventional SAS link. We used 16 flash SSDs to try to taxing LSI’s new 9200-series bandwidth, but imagine what would happen if 20, 30, or even 50 drives were attached through expanders and appropriate storage applications. The SAS link suddenly becomes the bottleneck.
SAS 6 Gb/s = Affordable Backbone for Virtualization
Also consider the SAN scenario. In environments where storage works independently from specific servers (through SAS or iSCSI), the downlink to your storage is key. Enterpises utilize heavy storage appliances to power virtualized system environments so that active operating system partitions can quickly switch from one server to another. iSCSI over Gigabit Ethernet remains the bottleneck, but once SANs are taken over by 10 GbE (or in Fibre Channel environments), SAS 2.0 will present a great opportunity to effectively double storage performance without much additional cost.
Decision makers in the process of finding new solutions should take the time to dig into SAS 6 Gb/s. It may be worth the investment compared to SATA hardware or a workable alternative for expensive Fibre Channel hardware.
