Re: hardware raid vs. software raid

On Thu, Nov 30, 2006 at 10:53:26PM +0100, Matus UHLAR - fantomas wrote:

I did not want to mention this, because:

- software RAID-1 has bus overhead (the same data have to be transferred
multiple times to multiple drives, so writing may be twice as slow)

This is only true if you use IDE and also put the mirrored pair on the
same channel (which would be incredibly foolish). Under every other
conceivable scenario, the system is smart enough to do both writes
simultaneously since they will be going difference places.

- software RAID-1 has high CPU and bus overhead in case of resyncing after
disk outage (hw raid does that itself)


Huh? I have built lots of RAID one systems and seen many of them
resync. They do have high I/O overhead (naturally, since it is a
resync). However, I have never seen one produce high CPU overload. I
suppose if you forgot to enable DMA on your drives, or somehow managed
to disable it (it is enabled by default), then you might see high CPU
load during resync. But then, you would see high CPU load for anything
that does any significant amount of I/O.

Regards,

-Roberto
--
Roberto C. Sanchez
http://people.connexer.com/~roberto
http://www.connexer.com

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