Re: performance limitations of linux raid

[Christopher E. Brown]

On Thu, 4 May 2000, Michael Robinton wrote:
> > 
> >     Not entirely, there is a fair bit more CPU overhead running an
> > IDE bus than a proper SCSI one.
> 
> A "fair" bit on a 500mhz+ processor is really negligible.


        Ehem, a fair bit on a 500Mhz CPU is ~ 30%.  I have watched a
*single* UDMA66 drive (with read ahead, multiblock io, 32bit mode, and
dma transfers enabled) on a 2.2.14 + IDE + RAID patched take over 30%
of the CPU during disk activity.  The same system with a 4 x 28G RAID0
set running would be < .1% idle during large copies.  An exactly
configured system with UltraWide SCSI instead of IDE sits ~ 95% idle
during the same ops.

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