[CentOS-virt] Slightly OT: FakeRaid or Software Raid

Christopher G. Stach II cgs at ldsys.net
Thu Dec 3 05:48:57 UTC 2009

----- "Grant McWilliams" <grantmasterflash at gmail.com> wrote:

> Interesting thoughts on raid5 although I doubt many would agree.

That's okay. We all have our off days... Here's some quality reading:


Maybe you are thinking of RAID 6.

> I don't see how the drive type has ANYTHING to do with the RAID
> level.

IOPS, bit error ratio, bus speed, and spindle speed tend to factor in and are usually governed by the drive type. (The BER is very important for how often you can expect the data elves come out and chew on your data during RAID 5 rebuilds.) You will use those numbers to calculate the number of stripe segments, controllers, and disks. Combine that with the controller's local bus, number of necessary controllers, host bus, budget, and other business requirements and you have a RAID type.

> a RAID 10 (or 0+1) will never reach the write... performance of
> a RAID-5.

(*cough* If you keep the number of disks constant or the amount of usable space? "Things working" tends to trump CapEx, despite the associated pain, so I will go with "amount of usable space.")


Christopher G. Stach II

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