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As more and more organisations connect their data centres to remote disaster recovery sites, they are discovering the need to link SANs over WANs.

The problem is that SANs and WANs generally use incompatible technologies, making building a SWAN an expensive challenge - but that's changing now as a new breed of lower-cost SAN extension emerges to take advantage of IP-based WANs.

The primary driver for SAN extension is business continuity, but there are other factors pushing it, such as regulatory requirements which in some industries are forcing companies to move their main and backup data centres further apart.

The problem for anyone who needs to link two SANs is that while IP-based SANs are possible, using technology such as iSCSI, most existing SANs are based on Fibre Channel.

Taking the Metro

Until recently, the common way to link Fibre Channel networks was over DWDM fibre or via a SONET/SDH service. Those are expensive though, and are now being undercut on price by WAN and Metro Ethernet services.

That's also enabling smaller organisations to get involved, says Nortel product manager Michael Arno: "SAN extension has been more on the core, for large enterprises and so on. Now it's more Ethernet and IP connectivity."

He adds that Nortel's latest BCS3000 - for business continuity solution - is "small and more flexible, so for example you can have Fibre Channel and Ethernet in, and WAN Ethernet out - you can go 2000km over WAN Ethernet." The device has three slots for port modules, allowing it to have up to 12 ports client-side and 6 WAN-side.

PacketLight is another company that recently launched into the business of extending SANs over IP, says its marketing VP, Avi Katz.

"We were using Fibre Channel over SDH and DWDM, now we're introducing our first FCIP product, the PL-200," he says.

The PL-200 is a bridge, using a protocol called FCIP - Fibre Channel over IP - which allows it to tunnel SAN traffic through an IP network such as Ethernet. Why take that route instead of a pure-IP route such as iSCSI?

"Different customers have different needs, even in IP," Katz acknowledges. "But iSCSI is thousands, Fibre Channel is millions."

Encapsulate, don't convert

FCIP bridges SANs not by converting the SAN data, but by encapsulating Fibre Channel packets in Ethernet. Katz says the PL-200 can also do forward error control, rate-shaping and prioritisation. "A lot of this has traditionally been software, we're now applying hardware to do tasks such as compression.

"It supports 2Gig on the Fibre Channel side, 1Gig Ethernet on the uplink - 67 percent of metro Ethernets are 100Mbit/s or less so throughput is much lower over the WAN. It includes encryption, which is a must for IP, and we will add compression."

There is one other way to connect storage over IP besides FCIP and iSCSI, and that's iFCP, which is a routing protocol. Katz acknowledges that there could potentially be issues with bridging rather than routing, as there can be stability issues with very large and non-segmented SANs.

"FCIP tunnels over IP so it makes it all one big SAN," he says. "That might be an issue for larger companies with many SANs - they might need routers instead.

"There is an issue with delay too - it's higher with IP than DWDM so your applications may need to be configured to cope."

Michael Arno agrees that FCIP is the way to go. He points out that not only did Nortel have an investment in iFCP developer Nishan Systems, but it co-authored iFCP. (Nishan was bought by McData and its iFCP technology forms the basis of McData's Eclipse line.)

He says Nortel chose encapsulation for the BCS3000 for performance reasons - it tested iFCP and found it too processor-intensive.

New applications, not new tech

Of course, FCIP is hardly new - it's been around for several years and is already offered by the likes of Brocade, Cisco and McData. However, it's mainly been offered as part of a switch or director, claims Avi Katz.

"The competition is FCIP-capable switches from Brocade and Cisco - they are good for new SANs, but if you already have the SANs and want to connect them, that's an expensive route," he says. "For example, a Brocade 7500 might cost $30,000, but a PL-200 is around $10,000." And whichever vendor you choose, you'll need an FCIP-capable box at each end of the WAN.

Michael Arno agrees, though he points out that the BCS3000 is more than just a SAN bridge in any case. What Nortel has come up with is a three-slot chassis able to house a variety of modules - in effect, a mini-director - but still at a relatively low price.

"It's $12,500 for the chassis and one four-port module," he says. "There's also a data acceleration module - a WAFS-type server for branch consolidation that uses the Tacit software."

Arno adds that Nortel is looking at a six-monthly release schedule for new versions of the BCS3000 software. Among the additions planned for version 2 in early 2007 are TCP acceleration functions from Packeteer, and encryption.

One possibility for the future is that the whole FCIP thing could simply be embedded into the WAN, suggests Avi Katz. He foresees service providers and telcos buying the boxes so they can offer SAN extension as a premium service complete with the necessary hardware.

He adds that storage networking "is a very conservative market. I come from a networking world, which is much more open."