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Table Of Contents  CertiGuide to A+ (Core Hardware)
 9  Chapter 0100:  Hard Drives
      9  IX  RAID

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JBOD

The number of ways to gang up drives in arrays beyond what has been described (so we will buy more drives) is amazing. All sorts of RAID X numbers have appeared.

And the most honest term that has come out for some controllers is known as JBOD. This is short for Just a Bunch Of Disks.

[spacer]Interleaving

As hard drives spun (compared to floppies) very quickly, the sectors of the track would 'fly past' the read/ write head very quickly. The head could read say, sector 1, and pass the data off to the controller.

Well, even at 3,600 RPM, sector 2 came by really fast. Too fast for the controller to do any more processing. That would mean wait for an entire rotation to complete. Now the controller is waiting around (too long). Solutions require more solutions it would appear.

The solution was called interleaving. By storing the data in sectors such as 3, 6, 9 etc. it gave the controller a chance to catch up. The interleaving could just as well have been in the example, 6, 12, 18 etc. The ratio of these number is known as the interleave ratio. As you may have guessed, the smaller the ratio, the faster the controller has to be, to be able to process the data, and the faster the drive can send and receive data.


Before closing this chapter, a few loose ends should be covered. This is not so much for the A+ certification test, but rather the ultimate test of successfully performing in the real world.

Drives are Hot

Today, drives are 1:1 interleave, and are fast, cheap storage. Some might use the slang term, hot. Some drives are literally hot. An old or large drive may burn you if you touch it while in operation.



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