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Design concepts for storage networks: Part 3

Bits & Bytes: Design concepts for storage networks: Part 3 "in-band ESCON"

The "In-band ESCON" model

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

"In-band" technology is nothing new. Many devices used for connectivity in computing are "in-band". For example, an Internet router that sends data traffic around the world utilizes a form of in band virtualization. Yet when some in the storage industry combine the terms "in-band" and "virtualization" into one phrase and apply it to storage, they would have us think global data destruction is imminent. Nothing could be further from the truth.

In fact, the storage community already extensively uses this technology in different forms. Almost all of the storage array vendors place virtualization on the front end of their storage arrays for LUN management. This technology is so well accepted that it is used extensively in highly available data centers. So, while not all in band solutions are created equal, we would not have the SANs we have today without this technology.

In regards to the term 'ESCON', it comes from the mainframe world and refers to the highly available, though relatively simple to configure, black box that connects servers and storage devices. These two terms, "in-band" and ESCON, combine to create the second storage networking model, the "in-band ESCON" model.

"In-band" only becomes controversial because it moves the storage intelligence into the network appliance. It manages the data on different storage arrays from different vendors while creating a central console to manage storage for the entire enterprise. What it does not natively offer is end-to-end performance management solutions required in some environments.

This architecture lends itself well to storage environments of 40 servers or less with multiple servers, different OSes or storage arrays from different vendors or both. It also allows someone to manage an environment with less control over all aspects of the storage network.

In the next column we will look at the third model where one has a rapidly growing environment necessitating switches that are not so simple to configure and design.

Read Part I: Design concepts for storage networks

Read Part II: Out-of-band ESCON

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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