Bangkok--20 Sep--Core & Peak
For all the recent interest that surrounds Serial Attached SCSI (SAS), it is not a new technology. Neither is it a brand new concept.
The word “serial” comes the use of point-to-point serial protocol to transfer data. This replaces the slower parallel SCSI bus technology that appeared in the mid-80s. The same concept is now used for the next generation of ATA drives: Serial ATA.
Enterprise disks with SAS interfaces have been shipped since 2004. They began life as replacements of hard disk drives within servers, rapidly replacing the slower SCSI drives. With the availability of 3Gbps and 6Gbps SAS, performance is now on par with Fibre Channel (FC) design and re-ignited the question of whether SAS will replace FC.
Increasing shipments
This tussle between SAS and FC has been played out in the media and technical circles for sometime. FC is entrenched in the enterprise storage space and replacing it may not be that simple. But SAS is already seeing interest in both large enterprises and small and medium enterprise market space. With developers and technology firms like Hitachi Data Systems embrace SAS in their design, SAS adoption is only set to increase.
According to IDC 2009 projections for worldwide HDD shipments for Enterprise Applications, 2008-2012, SAS drive shipments are slated to increase in the next three years while FC drive shipments are expected to decline.
It is not just analysts are projecting SAS’ rise at the expense of FC. Today’s disk vendors are also planning to limit their development of new FC disks in the next few years. That means that FC disk development will be capped at 600GB and a 4Gbps interface. Meanwhile, SAS drives are expected go beyond 6Gbps (See table for the benefits of 6Gbps SAS drives).
New variable to performance: cost
One of the key reasons for the favorable analysts’ predictions for SAS lies in one simple factor: it continually demonstrates a better price performance ratio.
Before the economic downturn, large enterprises were concerned with purely performance. Now enterprises regardless of size are experiencing huge budget constraints; price performance is now a sought after benchmark in storage. It is also an area where SAS is designed to outshine its rivals.
The difference in cost effective performance can be readily seen in the recent Storage Performance Council (SPC) Benchmark-1 results. During the non-profit organization’s testing, Hitachi Adaptable Modular Storage 2500 achieved the fastest throughput results among all midrange storage competitors with dual controllers with an impressive throughput result of 89,491.81 SPC-1 IOPS and an 8.98 millisecond average response time. The price-performance ratio of these results was a very low US$6.71/SPC-1 IOPS.
Taken at face value, these values represent a huge savings for businesses—especially small and medium enterprises that are very price averse. Traditionally, businesses have achieved high performance by purchasing powerful yet costlier systems and/or employing specialists to optimize the performance.
SAS-based designs provide cash-strapped enterprises a lesser expensive alternative solutions without sacrificing performance. Essentially, they offer savings in both capital and operational expenses, allowing smaller companies to enjoy the performance of high-end storage systems at a price point that is palatable to their budgets.
Backward compatibility with SATA
Another cost benefit of SAS is its backward compatibility with Serial ATA (SATA) disks. Essentially, SAS’ backplane design and protocol interface allows the use of both SAS and SATA drives in the same system.
For integrators and customers, this is certainly good news. First it provides flexibility and freedom to use SATA, SAS or a combination of both. For the price-sensitive small and medium enterprises, it allows the administrators to upgrade their SATA drives to SAS drives when demands dictate it, without worrying about drive compartment sizes or cabling.
Yet, perhaps the most significant cost benefit is the ability to mix and match different drive types appropriate for the application itself. So for cost-sensitive nearline storage applications, the slower and half duplex SATA drive can be used or even reused. The more expensive but high performance and full duplex SAS drives can be allocated for mission critical applications.
SAS’ backward compatibility with previous-generation SCSI software and middleware coupled with its use of expander hardware as a switch also make it easy to incorporate legacy components, hosts, and drives into evolving SAS designs. This minimizes or even eliminates further training or integration costs and the need for costly modifications to legacy software.
Conclusion
By combining the proven reliability and functionality of parallel SCSI with the performance and design advantages of serial storage technology, it is easy to see the appeal of SAS-based storage systems.
In the end, it will be a simple question of economics. Regardless of size, businesses will be increasingly forced to consider better price performance when selecting storage architectures—especially with new regulations that require more data to be available for longer periods. Although FC will continue to play a prominent role in enterprise storage systems for sometime to come, SAS’ better price-performance ratio and backward compatibility with SATA and legacy components will increasingly persuade IT administrators to built optimized SAS storage architectures that streamline costs.
In the near term, the small and medium enterprises will benefit from SAS. SAS essentially provides these price-sensitive businesses with the ability to enjoy enterprise-class storage at much more budget-friendlier prices.