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EMC: McData's Trunking Needs Work

Based on its internal testing, EMC Corp. (NYSE: EMC) says it won't support McData Corp.'s (Nasdaq: MCDTA) Open Trunking yet because of a performance-related issue it discovered with the feature, according to an EMC product release note obtained by Byte and Switch.

EMC's release note for the Connectrix Manager version 7.01.00, dated April 2003, describes its testing of McData's Open Trunking, which monitors traffic on multiple interswitch links (ISLs) and dynamically reallocates bandwidth depending on traffic patterns. (Connetrix is EMC's line of rebranded Fibre Channel gear.)

McData's Open Trunking feature load-balances traffic across multiple ISLs and is supposed to support both McData and non-McData switches. The feature became available with the release of McData's Enterprise Operating System (E/OS) firmware version 5.0 in March 2003.

But EMC, in its eLab test of the E/OS 5.01 firmware, says that there can be as much as a 50 percent chance of "frame out-of-orders on each reroute" when switches are interconnected using Open Trunking -- resulting in significant congestion. (A reroute occurs when an ISL becomes overloaded.) Typically, when switches detect that frames have been transmitted out of order they try to resend the data, which EMC says "may take from several hundred milliseconds to 60 seconds (the driver's ULP [upper-layer protocol] timer) to initiate."

"The high rate of out-of-order [frames] and the long duration of the retries has resulted in eLab's decision to not support McData's Open Trunking at this time," says EMC's release note. "McData engineering is investigating options to significantly lower the out-of-order-to-reroute ratio. No conclusions have been reached on the viability of these options."

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