Stretching SANs

3:00 PM -- SAN extension is one of those terms, like dating or rock 'n' roll, that you think is nailed down -- until it turns out to mean something entirely different than it used to.

In the old days (like two years ago), SAN extension meant the ability to carry Fibre Channel SAN traffic across Sonet or DWDM links, sometimes using telecom and optical networking equipment, and sometimes using channel extenders from the likes of CNT (now McData). The reason for SAN extension seemed logical -- to overcome the distance limitations imposed by the data center.

Now that definition could be pass. "SAN extension is a misleading term. It is the application's data replication requirements over the WAN that's at issue. You do not access SAN attached storage over a WAN," reports one analyst, who asked not to be named.

This analyst thinks IP networking is the real force behind WAN replication, and he believes that encapsulating Fibre Channel into IP networks (à la FCIP or iFCP) will be replaced by iSCSI and IP SANs by the end of this year.

Others beg to differ. Companies like ADVA, Ciena, Meriton, Nortel, and PacketLight find business booming amongst enterprise customers who are, in fact, extending local SANs across metropolitan areas. Fibre Channel is the vehicle in most cases, not IP."The SAN manager buys storage extensions over Sonet and over local DWDM where they can afford it," says Stephen Barr, director of solutions sales at Ciena. According to him, nearly all of the customers who buy Ciena gear for these purposes use Fibre Channel. For them, the issue is guarding against packet loss to ensure data integrity in real time, even over metro Ethernet services.

Mark Smith, president of Centrepath Networks, which helps companies build and operate private optical and storage metro networks, saw business grow 75 percent in 2005, largely on the basis of folks extending Fibre Channel SANs across optical fiber in metro areas. "Seventy-five percent of our networks are storage related," he explains. Though disaster recovery is a popular application, Smith insists that four out of five customers are simply looking to extend protocols like EMC's SRDF synchronously across multiple data centers.

What do you think? Is SAN extension part of the dead language of IT? Is it an IP issue, not a Fibre Channel one? Has the storage world grown too complex to cover it? Weigh in on our latest poll. We'll see just how far you've extended the meaning -- and usefulness -- of wide-area storage.

— Mary Jander, Site Editor, Byte and Switch

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