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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, uhlar@fantomas.sk ; http://www.fantomas.sk/
Warning: I wish NOT to receive e-mail advertising to this address.
Varovanie: na tuto adresu chcem NEDOSTAVAT akukolvek reklamnu postu.
I just got lost in thought. It was unfamiliar territory. 

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