Can SAS Replace Fibre Channel? - EnterpriseStorageForum.com

Can SAS Replace Fibre Channel?

"In three years, SAS will completely replace Fibre Channel," was the bold prediction made earlier this month by Patrick Rogers, vice president of solutions marketing at Network Appliance (see Storage Vendors Move Down Market).

"SAS technology — comprising both SAS disk drives and SAS drive controllers and interconnects — provides significant end user benefits and represents the next evolution in enterprise storage," said Rogers.

In his view, NetApp stands at the forefront of this trend via its recently announced FAS2000 products. However, he admitted it will take some time for a complete transition to occur and for the technology to fully mature. While the underlying disks are the same as Fibre Channel disks (i.e., the same media, heads and reliability — only the interfaces differ), the Serial Attached SCSI (SAS) link speeds are still lower than FC disks. But SAS has the advantage of being able to accommodate both high-performance SAS HDDs and high-capacity SATA disks in the same infrastructure.

"The technology needs to mature beyond entry platforms targeting mid-size enterprises, where most of the SAS products are offered today," said Rogers. "While FC will continue to be deployed in large enterprises in the near-term, the drive vendors will be minimizing their investments in the FC interface after 2010. After all, the underlying drive technology is the same — it's just the interface (including HDD firmware) that's different."

Not everyone is in agreement with the NetApp view, however. John Lallier, vice president of technology at FalconStor Software, believes that SAS completely replacing Fibre Channel disks in three years is no more likely than what was said a few years back about iSCSI replacing Fibre Channel interconnects.

"SAS will certainly take a portion of the installations that would otherwise have gone to Fibre Channel, but for the foreseeable future the two technologies will co-exist," said Lallier. "The simple fact is that no matter what advantages there may be in a specific technology, it still takes time to develop the level of trust and familiarity to warrant a complete changeover."

FalconStor's approach, therefore, is to parallel the way these things tend to pan out in the real world; i.e., users will have data centers with multiple technologies. In such environments, Lallier believes the most important point is to provide tools and services that are independent of protocol or hardware. That way, users have the ability to choose among the different technologies without having to sacrifice features. Thus, FalconStor plans to include support for SAS in the same way that its existing software supports Fibre Channel, iSCSI and InfiniBand.

"SAS needs to provide the same level of management integration that people now have with Fibre Channel," said Lallier. "This isn't a technology issue, but rather a question of support across various tools. Time is needed to make people as familiar with SAS as they already are with Fibre Channel."

Tam Dell'Oro, an analyst at Dell'Oro Group, is another doubter. Like Lallier, she doesn't think SAS will compete with FC.

"SAS isn't used to interconnect arrays with servers," said Dell'Oro. "It is mostly used to connect from array to array."

She defers to Emulex to answer why it hasn't been used between the array and the server. Mike Smith, executive vice president of worldwide marketing at Emulex views SAS as a complementary technology to Fibre Channel. SAS plays a role behind the array within the drive connections and in direct attach environments (between one array and server), but it does not play a role in the SAN (between one array and multiple servers). However, SAS is expected to replace SCSI in the back-end of the array.

"The reason is that SAS, and for that matter SCSI, currently has nothing in its protocol that allows SAN connectivity," said Smith. "The SAS industry is currently working on protocols for traditional SAN functions, such as zoning, but it is still unclear if SAS will ever play a role in the SAN, and certainly not in the next three years."

Future Uncertainties

With NetApp bullish and the others doubtful, it remains to be seen just how much progress SAS will make in encroaching onto FC turf. What we can look forward to, at the very least, is plenty of new advances in SAS on the immediate horizon. Look out, in particular, for the addition of high-capacity 7200 RPM disk drives into SAS fabrics, along with the high-performance 15,000 RPM SAS drives being offered today.

"You'll see the migration of the technology deep into portfolios of enterprise storage solutions — including 6 Gb link speeds," said Rogers. "You'll also see supported array capacities grow markedly as the largest storage controllers begin supporting SAS."

What that adds up to, according to Rogers, is a gradual maturation of the SAS ecosystem and an adoption curve that may prove to be similar to what the industry went through migrating from parallel SCSI to FC storage.

Others, though, see upcoming technologies stealing the thunder from SAS. Dell'Oro, for instance, considers Fibre Channel over Ethernet (FCoE) to be a more compelling candidate as it enables users to merge their storage and enterprise networks. She reasons that Ethernet is used even in the smallest organizations and it is easy to hire IT guys for it. FC, on the other hand, is more sophisticated and fewer people know how to operate it. At the same time, government regulation requires more backups and access of files yet budgets aren't extended enough to import an FC infrastructure. These people are faced with the puzzle of figuring out how to comply without having to train people in FC.

"The solution might be to do some of their storage backup on Ethernet and send only important files on the FC network," said Dell'Oro. "That is the promise that FCoE holds, though products are not yet out on the market."

She expects the likes of Emulex, Brocade, Cisco and QLogic to be at the forefront, with the first products appearing sometime in the 2009 timeframe.

Emulex's Smith said FCoE would enable SAN traffic to be natively transported over 10Gb/s Ethernet networks, while leveraging the investment that customers have made in storage networks.

FCoE, he said, would give customers a new choice for more pervasive SAN connectivity in the data center. It would complement existing connectivity and protocols used in storage and data center networking. User benefits of this future technology include being able to leverage the existing base of OEM-qualified Fibre Channel drivers and management tools.

"FCoE enables SANs to utilize an industry-standard 10Gb/s Ethernet switch infrastructure," said Smith. "It also offers the opportunity to converge network traffic and storage traffic on a single HBA."

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