John-Mark Gurney gurney_j at
Wed Aug 18 23:28:51 PDT 2004

Greg 'groggy' Lehey wrote this message on Thu, Aug 19, 2004 at 15:52 +0930:
> > Your quoted text also seems a bit subjective as there are very valid
> > reasons for RAID-3, especially if one is looking for consistent
> > low-latency transactions like in video recorders and servers.
> Well, I did use *exactly* this example.  I also pointed out that the
> relative performance of modern disk subsystems is adequate for a
> single streaming video channel.
> Low latency depends on the number of concurrent accesses.  RAID-3
> handles concurrent access poorly, exactly because it accesses all
> disks for each transfer.

One thing that RAID-3 has is that you never have to do a READ/MODIFY
cycle when you do writes.  Until we implement a write-through cache
geom module, raid-5 will continue to substandard performance.

  John-Mark Gurney				Voice: +1 415 225 5579

     "All that I will do, has been done, All that I have, has not."

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