Report: Sonet's Tops for SAN Extension

IP continues to take a back seat to Sonet/SDH as a SAN extension method, mainly because it's not ready for synchronous mirroring, according to "SAN Extension: A Market in the Making," the latest report from Byte and Switch Insider, this publication's paid subscription research service.

IP isn't yet ready for fast data recovery. Instead, IP-based solutions are gaining traction in applications such as archiving data remotely on tape, for which no specific link is required between the data protected and backup copies, as is the case for data mirroring.

Other methods offer more reliability for data mirroring, though these also have pros and cons. Wave-division multiplexing (WDM), for instance, is currently the fastest and best-performing SAN extension method. But equipment is expensive and dark fiber, typically required for implementation, isn't always readily available.

Sonet/SDH, despite being the most widespread method, is operationally a hassle and expensive to scale. On the plus side, it offers robust management and quality of service. SAN extension also is evolving through Sonet/SDH improvements such as Generic Framing Procedure (GFP).

Not everyone agrees with the report's assessment of SAN extension methods. For example, Jim Morin, vice president of strategic planning for CNT (Nasdaq: CMNT), says that more than half the SAN extension products his company has shipped since 2002 had IP connectivity, compared to about 25 percent with Sonet, 15 percent with DWDM, and 10 percent with links to T1/T3 leased lines."Our experience shows that SAN over IP solutions are not just a promise, but are being widely deployed today," Morin says. He does acknowledge, though, that most IP solutions are used for asynchronous backup, or a combination approach in which customers use synchronous backup locally and asynchronous backup over long distances.

Morin also points out that customer choices often reflect factors such as pricing, fiber availability, and Sonet bandwidth, which differ with geography. "There are lots of anomalies," he says.

Besides weighing different SAN extension methods, the report explores alternatives provided by commercial products from a range of vendors, including:

Dave Raffo, Senior Editor, Byte and SwitchMore information about the current Byte and Switch Insider report, "SAN Extension: A Market in the Making," is available here.