[linux-elitists] Broken promises (was: The desktop in your pocket)

Brian McGroarty brian@mcgroarty.net
Thu Jan 29 07:25:56 PST 2004


On Wed, Jan 28, 2004 at 06:59:48AM -0800, Ben Woodard wrote:
> On Tue, 2004-01-27 at 19:29, Jeff Waugh wrote:
> > <quote who="Andrew">
> > 
> > > RAID5 is a different story; the amount of overhead in calculating the
> > > parity (yeah I know XOR) and writing *different* data to different disks
> > > is (IMO) significantly higher than straight-out mirroring.
> > 
> > s/significantly/marginally (and on modern cpus, mostly irrelevantly)/
> 
> In my experience, the problems with SW RAID even RAID5 may not show up
> with just a handful of disks and it is certainly not the CPU. The
> biggest problem is bus bandwidth. If you have the bus bandwidth to spare
> SW RAID is fine.

A side note: In my configuration at least, 2.6 made a significant
improvement in the speed of software RAID 5 on IDE devices. On my 8
volume RAID, the read speed is nearly half again as fast.

The machine also stays far more responsive when performing huge writes
to the RAID. It used to make the system all but unusable when I was
pulling down a large data set.
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