Re: SW RAID read performance

[Justin Piszcz <jpiszcz@lucidpixels.com>]

I've only ran the benchmarks on a single controller.  Run a test for me, 
read a lot of data on the drive and show us iostat -x -k 1 and see if it 
reads from both drives at the same time.

On Thu, 3 Aug 2006, Dave Ewart wrote:

> On Thursday, 03.08.2006 at 07:30 -0400, Justin Piszcz wrote:
>
> > > I have 2 disks in RAID 1 and I expected reading will be approx. 2x
> > > faster then a single disk reading because there can be used the same
> > > technique as on RAID 0. I tested it with bonnie++. Can linux SW RAID
> > > 1 read "in stripes" to boost the reading performance?
> >
> > From my benchmarking on my RAID1 (dual raptor RAID1) it appears it
> > reads from one drive or the other.
>
> It all depends on which disk controllers you're using and their
> throughput.
>
> I have two, separate SATA disks on two different SATA controllers and
> read performance in a RAID-1 configuration *is* (nearly) twice that of a
> single disk, in many situations.  I think I've got the benchmark
> statistics somewhere...
>
> If "it appears it reads from one drive or the other" is the case, then
> you probably have a bottleneck somewhere else.  Are these disks on the
> same controller channel?
>
> Dave.
>
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