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When is a SAN not a SAN?

There are other entities called SANs -- don't be confused.


When is a SAN not a SAN?
Rick Cook

In the world of Windows 2000, "SAN" means both "Storage Area Network" and "System Area Network." In spite of the similarity of the names, and the fact that they are often both referred to as SANs in Microsoft-land, they are quite different things.

The System Area Network enables very fast communication between servers running Microsoft's Windows 2000 Datacenter by using Windows Sockets Direct Path (WSDP) over a special 1 Gbps fibre-channel-based channels. A Windows 2000 System Area Network isn't concerned with storage at all and only links Datacenter Servers connected to a shared device running Microsoft Cluster Server.

A System Area Network eliminates the overhead associated with TCP/IP in connecting two servers. Applications based on Microsoft's Winsock can also use the network to connect from one Datacenter server to another.

Further confusion can occur because the physical layer of the System Area Network uses special System Area Network adapters which perform roughly the same role a Host Bus Adapter does in a Storage Area Network. However SAN HBAs and SAN adapters are not compatible.

Microsoft provides a description of System Area Networks and how they work in article Q260176 in the Microsoft Knowledge Base, available at Microsoft's web site.

Rick Cook has been writing about mass storage since the days when the term meant an 80K floppy disk. The computers he learned on used ferrite cores and magnetic drums. For the last twenty years he has been a freelance writer specializing in storage and other computer issues.

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