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.