Normalizing the SAN: Part 2

The definitions of the various and most common types of virtualization: host based, network based, and array based.

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Ed note: This is the second in the series of three articles on virtualization from First Data Corp's Sr. Information Systems Analyst, Jerome Wendt.

Normalizing the SAN: Part 2

Now for the definitions of the various and most common types of virtualization: host based, network based, and array based virtualization.

Host based virtualization is accomplished by putting a software agent on each server on the SAN. This software will, in theory, manage and share the storage between the different servers on the SAN that has this software agent loaded on it. This approach is also often referred to in the press as out of band virtualization. Veritas is the vendor most often associated with this approach in the Open Systems space.

Network based virtualization is accomplished by putting a device with software loaded on it that sits between the server and the storage. This approach is also referred to in the press as in band virtualization. All data that travels on the SAN between the server and the storage must pass through this device. This device recognizes all of the storage and servers and presents the storage in logical volumes to the servers. Originally championed by a number of small companies, Datacore, FalconStor and StorageApps most notably, this approach has since been formally adopted by Hitachi LTD, IBM and Fujitsu Software Technologies (Fujitsu Softek) as their strategic direction.

The third and most common virtualization approach is array-based virtualization. With this approach, an external cabinet houses all of the disk drives and then uses its own internal software to virtualize the disk behind it. This approach was originally championed and popularized by EMC in the 1990's though other disk vendors such as IBM and Hitachi Data Systems now have many of the same features as EMC.

So the question is, of these three technologies, which is the right choice? (The right choice being defined as the most cost effective, will allow you to use the investments you already have in place, and still scale for future growth. In addition, it will ideally simplify the administration of the storage.)

About the author:

Jerome Wendt is a Sr. Information Systems Analyst for First Data Corp. He is responsible for Managing and resolving performance related issues. Jerome is also responsible for exploring new SAN and open systems storage related technologies to solve business and technical problems in the data center.

Click to read the first installment of "Normalizing a SAN".

Part 3 of this tip helps you choose which virtualization technology is right for you.
This was first published in September 2002

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