Serial Attached SCSI to outperform FC

BANGALORE, INDIA: For all the recent interest that surrounds Serial Attached SCSI (SAS), it is not a new technology. Neither is it a brand new concept. However, it has come a long way in the past few years

The word 'serial' comes from 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.

Also Read: Can iSCSI win over FCoEs hype?

Enterprise disks with SAS interfaces have been shipping 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 in highly random read environments can outperform FC, all of which has re-ignited the question of whether SAS will replace FC.

SAS or FC: Which way to go?

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.

While SAS technology not only continuous to demonstrate better price performance ratio, it also reduces the power and space consumption up to 40 percent thus reducing total TCO.

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 who 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. Which 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).

6Gbps SAS features, benefits

Source: SCSI Trade Association

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Why SAS?

One of the key reasons for the favourable analysts’ predictions for SAS lies in one simple factor: SAS 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.

SAS-based designs provide cash-strapped enterprises a less expensive alternative solution 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. 

Another cost benefit of SAS is its 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.

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’ 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.

The author is director, pre-sales and solutions, India at HDS.