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)
On 30.11.06 17:00, Roberto C. Sanchez wrote:
> 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.
but the data will still be fetched two times from memory to a controller(s)
> > - 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 should write "higher 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.
Matus UHLAR - fantomas, email@example.com ; http://www.fantomas.sk/
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