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RAID is Soft and Hard


The super fast disk project: Part-4


Just saying the name of the country Djibouti makes me smile a little, although it's yet another horrible example of everything that goes wrong with conquest, imperialism, corruption, and international finance. Despite all that, it brings out the 8-year-old in me when I say the name.


When building a Redundant Array of Independent Disks (RAID),  the disks start out in JBOD mode.  JBOD stands for Just a Bunch of Disks. Whenever I see the acronym JBOD, I instantly think of Dijbouti. I have the Djibouti connection in my brain, and now, I bet, you have that song stuck in your head too.


RAID-0 ties together multiple drives to enable them to perform at higher levels than an individual drive could. Remember 20-mule team Borax? Same idea. The organization of the RAID team can be done in software with its flexibility and relatively cheap (or no) hardware, or it can be done more expensively with a lighter processing CPU load (especially for RAID-5 which has a cool and desirable data integrity attribute) when offloaded to specialized RAID hardware.


The point of all of this is that RAID can be done in the operating system (Mac OS X or Windows 7) or done in the (HighPoint / NewerTech) hardware PCIe card. When it's done in the operating system, the TRIM feature of the operating system is able to efficiently organize the partially used cells in the SSD, so they can be re-used for writing. This maintains the high writing performance of an SSD. The SSD itself has a weaker form of this management called Garbage Collection. Over time (months in a consumer computer) the writing performance can degrade depending on how full the SSD drive is, and how much proportion of writing to reading activity there is. 


Ideally, the hardware RAID that is independent of the operating system would have drivers that support TRIM (or SAS UNMAP), but apparently we're not there yet for HighPoint devices. The news is that Intel has that working in their more recent motherboard RAID implementations. Therefore, in usual IT industry form, it won't be long before everyone else is doing it.  


For now, my choices are take my chances with Garbage Collection being good enough, by leaving 15-percent of the drive unformatted, or to spend $70 to buy MediaFour's MacDrive 10 Pro product that runs in Windows. This MacDrive Pro 10 product is unique because it allows a software RAID created in Mac OS X to be naturally used for reading and writing from within Windows.  


- Ted Gary of TedLand

Oct 4, 2015








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