Re: FreeBSD 5.3b7and poor ata performance

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