Re: SW RAID read performance

[David Siroky <ml@dasir.net>]

Dave Ewart píše v Čt 03. 08. 2006 v 19:31 +0100:
> 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.
> 

My benchmarks have shown me ~45MB/s both on single drive and SW RAID 1
(so no speed up at all). I have UDMA133 PATA (it can theoretically
sustain speed over 100MB/s) controller so I would expect the SW RAID 1
will bring me at least more then 50MB/s when reading, right?

David