Why 42mb for HDP?

Submitted by Edward Branley on Wed, 09/21/2011 - 09:10

UPDATE: I use Networkedblogs to echo this site over to Facebook, which means my non-techie friends see it as well. When one of them saw the title of the article, she replied back, simply, "Because 42 is the answer. :-)

Architecture diagram for Hitachi Dynamic Provisioning (VSP/USPV)

Nigel Poulton offers some excellent speculation on why Hitachi Dynamic Provisioning uses a 42mb page size in HDP's Dyanmic Mapping Table. This graf is very curious:

Interestingly, you can also divide 42 by 2,3,4,6 and 7. These numbers equate to the number of data spindles in all basic supported RAID configurations (not including previously mentioned concats). To be honest, knowing a little about how clever, efficient and thorough the developers in Japan are I expect that the 42MB Page size maps to a lot more internally. In fact I wouldn't be surprised if the number of screws used to build each internal disk chassis was divisible by 42….. ;-)

"clever, efficient, and thorough..." Yes, they are!

If you work with USPV/VSP, this is a very interesting read.

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About Edward Branley

Edward Branley is a freelance author, consultant, trainer, and procrastinator. He spends a lot of time as an Instructor (contract-Merit Systems) for HDS Academy. Edward started teaching at this level in the 1990s for Digital/Compaq, teaching Tru64 UNIX and TruCluster courses. He first taught for Hitachi Data Systems in 2005, doing the pilot of THI0515, Modular Storage Foundations. He also conducted the first 3T (Train-The-Trainer) class for THI-0517, Enterprise Storage Foundations, for HDS Academy (EMEA).

In addition to the certification classes, Edward teaches a wide range of subjects for @HDSAcademy, including Hitachi Command Suite, Tuning Manager, Enterprise (VSP) Hardware Install/Config, Modular (AMS) Install/Config, and all of the company's replication products.