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Design concepts for storage networks: Part 2

Design concepts for storage networks: Part 2 -- the out-of-band ESCON model

The out-of-band ESCON model

This column defines the first of five storage networking architectures, the "out-of-band ESCON" model, which represents the one found in many storage networking computing environments today. This model possesses three distinct characteristics. First, it reports on what data resides where on the storage devices. Second, it tracks the path of the data through the storage network. Third, it utilizes a relatively simple switching technology.

The term "out-of-band" is a fairly simple concept to understand. Simply put, when one sees the "C:" drive on your PC, you are having an "out-of-band" experience for the "C:" logically represents the actual physical path to the underlying disk.

Yet this concept gets complicated very quickly in a networked storage environment. While the "C:" prompt may represent the logical path to the disk, it neither maps out the physical path to the disk nor does it report on which storage device the data resides. For today's storage administrator, that's unacceptable.

To be effectual, the storage administrator needs to know not only on which storage devices that the data resides but the path it follows through the storage network. Here is where a server sitting "out-of-band", or outside of the data path, gives the storage administrator the ability both to report on and manage these critical storage components.

The term 'ESCON' comes from the mainframe world and refers to the black box that connects the servers and storage devices. This black box lacks advanced intelligent features such as routing or quality of service. However, they feature high uptime and reliability with relative ease of management that make these devices so desirable. Due to these features, this solution frequently gets deployed.

These two terms, "out-of-band" and ESCON, combine to create the first storage networking model, the "out-of-band ESCON" model. The "out-of-band" server manages both the data and data path utilizing agents placed on the servers as well as the API's of the respective storage networking components. This technology enables the storage administrator to configure any of the storage networking components, be it the server, the ESCON switch or the storage device on which the data resides. This architecture lends itself well to environments of 40 servers or less where one has a relatively good deal of control over all aspects of the storage networking environment.

In the next column we will look at the next model from the perspective where the data is managed in the data path.

Read Part I: Design concepts for storage networks

About the author

Jerome Wendt is a independent writer and storage analyst specializing in Open Systems storage and storage area network technologies. He currently manages storage and explores new storage technologies for a large organization in this capacity. Jerome may be reached at

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