Cisco Ups Multivendor Support

Cisco Systems Inc. (Nasdaq: CSCO) today announced it will offer Fibre Channel Network Address Translation (FC NAT), a technique for enabling routing of data between SANs from different vendors (see Cisco Consolidates Across Fabrics).

Cisco will make FC NAT available in its MDS 9000 SAN-OS 2.1 software, which is being qualified by storage vendors and should be available next month. Ciscos support of FC NAT means its MDS switches can manage other vendors’ switches connected to the MDS.

Brocade Communications Systems Inc. (Nasdaq: BRCD) and McData Corp. (Nasdaq: MCDTA) already offer FC NAT in their multiprotocol routers (see When a Router's Not a Router).

FC NAT translates domain addresses between SAN devices, allowing switches from different vendors’ SANs to communicate. Without FC NAT, the addresses must be changed manually, a time-consuming process that often requires rebuilding driver files.

Now that the big three switch vendors support FC NAT, SAN islands can be connected into one big happy SAN, right? Not exactly. Issues remain over how effectively switches work with FC NAT, and the vendors differ in their views about how important it is to share resources among disparate SANs.Brocade, with the largest switch installed base, doesn’t think it’s always a good idea to have different vendors’ switches talking to each other directly. Like McData, Brocade handles FC-NAT through multiprotocol routers that tie the SANs together, and Brocade product manager Mario Blandini claims that before FC routing, sharing resources by merging different SANs was possible but not practical.

“No one really does that in real life,” Blandini says. “Customers want to maintain different business units, running in native mode instead of in degraded [interop] mode.”

Cisco apparently hears a different message coming from customers. “It’s important now that SAN islands talk to each other,” Cisco's product marketing manager Rajeev Bhardwaj says. “And we see a lot of customers deploying SANs over distance now.” He says customers increasingly want to tie together SANs that have sprung up in different departments over the years, or heterogenous SANs at different sites that resulted from mergers or acquisitions.

Performance is another contentious issue. Cisco only supports QLogic Corp. (Nasdaq: QLGC) blade switches in native mode -- no surprise, considering the two are expected to announce an OEM deal where QLogic provides Cisco with 4-Gbit/s switches (see Cisco & QLogic: Headed for Huddle). Brocade and McData switches must be set to interop mode to work with Cisco switches, resulting in a performance hit.

Cisco's Bhardwaj admits switches “dumb down” in interop mode, but says the only significant problem is they don’t allow trunking.Blandini says, depending on the switches, they lose other features in interop mode, such as advanced zoning. Switches also have to be shut down and reset to go into interop mode, causing downtime.

How interoperability improves -- or doesn't -- among the switch vendors remains to be seen. In the interim, users have some tradeoffs to consider, and many will no doubt have requests, complaints, and suggestions for their vendors of choice.

— Dave Raffo, Senior Editor, Byte and Switch