FreeBSD 5.3b7and poor ata performance
Scott Long
scottl at freebsd.org
Mon Oct 25 14:27:19 PDT 2004
Brad Knowles wrote:
> At 2:45 PM -0600 2004-10-25, Scott Long wrote:
>
>> RAID-0 yes, RAID-10 no, at least not for software RAID. The machine
>> winds up having to transfer the same data twice across the PCI bus,
>> twice through the controller, etc. If the controller is on a simple
>> PCI-32/33 bus then it will quickly become saturated.
>
>
> I can't speak for GEOM, but my experience with vinum is that
> software RAID, especially RAID-1+0 will totally smoke the bare hardware,
> and will smoke most any PCI hardware RAID controller you put it up against.
>
> Granted, my experience is a few years old, so if you've got any more
> recent data that shows in detail what the current situation is and
> explains why, I'd love to see it. Until then, I stand by my results at
> <http://www.shub-internet.org/brad/FreeBSD/vinum.html>.
>
Software RAID does indeed have less latency than PCI RAID, and will
often result in higher performance. But as was said, there is always
a performance vs. reliability tradeoff. And when you are talking about
RAID-10 with a bunch of disks, you will indeed start seeing bottlenecks
in the bus.
Scott
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