[Pc_Support] 3Ware question

[Jason Boxman]

Bryan J. Smith said:
> Jason Boxman <jasonb at edseek.com> wrote:
>> For software RAID 1 you'd have to send writes down the bus for each
>> drive, right?
>
> Correct.
>
> It actually should _not_ saturate the bus too bad during writes
> because of that.  But it _will_ saturate the bus during reads because
> it will interleave them.
>
> If you're using software RAID to a SATA PCIe x1 channel, then you
> should avoid this -- despite the redundant write.  The problem is the
> legacy PCI I/O, not software v. hardware.

I completely didn't follow.

What's the performance penalty for running software RAID 1 over hardware
RAID 1?  I thought it was purely duplicate data being written to each disk
instead of only once to the controller to mirror to each drive itself?

It sounds like software RAID 1 reads the same data from both drives for a
read, but ends up throwing one of the reads away?  I don't follow?