Re: Performance Characteristics of All Linux RAIDs (mdadm/bonnie++)

[Bill Davidsen]

Alan Cox wrote:
> On Wed, 28 May 2008 18:34:00 +0200
> "Jens BÃckman" <jens.backman@xxxxxxxxx> wrote:
>
> > On Wed, May 28, 2008 at 10:53 AM, Justin Piszcz <jpiszcz@xxxxxxxxxxxxxxx> wrote:
> > > Results:
> > >
> > > http://home.comcast.net/~jpiszcz/raid/20080528/raid-levels.html
> > > http://home.comcast.net/~jpiszcz/raid/20080528/raid-levels.txt
> > Either the RAID 1 read speed must be wrong, or something is odd in the
> > Linux implementation. There's six drives that can be used for reading
> > at the same time, as they contain the very same data. 63MB/s
> > sequential looks like what you would get from a single drive.
>
> Which is fairly typical of a cheap desktop PC where the limitation is the
> memory and PCI bridge as much as the drive.
I really don't think that's any part of the issue, the same memory and 
bridge went 4-5x faster in other read cases. The truth is that the 
raid-1 performance is really bad, and it's the code causing it AFAIK. If 
you track the actual io it seems to read one drive at a time, in order, 
without overlap.

--
Bill Davidsen <davidsen@xxxxxxx>
  "We have more to fear from the bungling of the incompetent than from
the machinations of the wicked."  - from Slashdot

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