Microsoft Walks Multipath

Since much of the server-based storage targeted for consolidation on Internet Protocol storage-area networks (SAN) resides on departmental servers running Windows, Microsoft's commitment to iSCSI has been key to the success of IP SANs so far.

The company began offering an iSCSI driver, or "initiator," for Windows 2000 Server, Server 2003 and XP Pro shortly after the standard was final in 2003. In February, Microsoft stated it would release late a new version that supports multipathing, a technology common in Fibre Channel SANs that supports load balancing and fail-over by allowing multiple connections, or paths, between servers and storage devices. Previously, Microsoft offered only multipath I/O (MPIO) for Fibre Channel, although Network Appliance and EqualLogic adapted it for their iSCSI products.

Microsoft's goal is to simplify block-based networked storage by providing a universal initiator and MPIO interface for Windows servers. "In the Fibre Channel world, there are a lot of proprietary solutions, and they can get quite difficult to troubleshoot," says Claude Lorenson, a senior product manager at Microsoft's Windows Server division. To avoid that situation, Microsoft will support only its own MPIO mechanism for iSCSI, although Lorenson says it will continue to support "legacy" MPIO schemes for Fibre Channel.

Tom Clarke, director of SAN technology at McData, wonders whether users will adopt MPIO. He says users adopting iSCSI for second-tier applications are more concerned about price than performance. "So will customers really want to deploy redundant pathing ... or will they conclude that single pathing is adequate?"

Uptime is the key, says Ramesh Viswanathan, director of computer and network administration at Siemens Corporate Research. "That is the one thing in the back of my mind: What is my fail-over strategy on this thing? MPIO would almost be a necessity for me," he says.

Jim Tarala, CIO and chief technology officer at Schenck Business Solutions, a beta user of MPIO, concurs. "We'll be taking that live. If I lose one iSCSI adapter to a server, it just fails over to the other and the user wouldn't even know," he says.

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