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Sun began to flesh out its server/storage convergence strategy last week when it unveiled a framework for turning its OpenSolaris servers into storage arrays with a utility called the Common Multiprotocol SCSI target for Solaris (Comstar).
The first edition of Comstar, available for the Build 90 version of OpenSolaris and scheduled to become part of the general OpenSolaris distribution in its next major release in November, allows customers to create a Fibre Channel array using a repurposed server and Fibre Channel host bus adapters (HBAs), according to Scott Tracy, director of storage platforms for Sun's software group. So far, Sun has qualified HBAs from QLogic Corp. and Emulex Corp.
Comstar brings the SCSI command set into the OpenSolaris kernel, rather than letting it run in "user-land" above the operating system. According to Tracy, this can help with the target's performance because it doesn't have to traverse the operating system and application memory for I/O to disk. However, Comstar does use some of the server's CPU, which might cause a performance hit over a typical Fibre Channel device, depending on how it's deployed.
Sun has further plans for the Fibre Channel target, including the creation of multiprotocol arrays based on its servers once the other protocols are integrated into Comstar. In addition, Comstar will eventually allow concurrent multiprotocol access to LUNs, Tracy said. While there are other items on the roadmap that pushed Sun to support Fibre Channel first, Tracy declined further comment.
Tom Trainer, an analyst with Analytico Inc., pointed out a downside to Sun's Comstar strategy: the potential performance hit of sharing the CPU. Tracy disputed this assessment. "The target CPU must run to process IO's," he said. "Every FC array does this. It will not cause a performance hit over typical FC device."
Another possible caveat for Trainer was that Sun won't issue a new warranty for server hardware repurposed for storage--repurposing the hardware won't change the warranty, according to Tracy, but that means it won't be extended, either.