software raid and multiple cores

[Mark van Harmelen]

Thanks Peter,

Your description of my question was spot on :) thanks.
Luckily we dont have those discs set up yet... I shall enquire further on
linux-raid as to what experimental might actually mean in this context.

regards
mark

On Mon, Nov 28, 2011 at 3:07 PM, Peter M. Petrakis <
peter.petrakis at canonical.com> wrote:

>
>
> On 11/26/2011 04:35 AM, Mark van Harmelen wrote:
> > Hi
> >
> > Thanks to those who contributed to a discussion on software raid
> > recently, it changed my mind about the universal desirability of
> > hardware raid cards.
> >
> > So now I'm intent on building a sw raid based machine, but mostly am
> > interested in performance under disc load.
> >
> > Basic question: given a number of spare cores (be they hyperthreaded
> > or not) is ubuntu's sofware raid clever enough to be able to deal
> > with multiple read and write requests simultaneously, one request per
> > spare core? Or would I expect only to see one of the spare core
> > utilised?
>
> Request level might be the the wrong level to look at, Linux already has
> lots of queue level optimizations. What's really going to matter here is
> efficiently handling parity calculations and the effective RAID
> real estate (stripes). There does appear to be a  multi-core optimization
> for MD RAID5/6 and it's disabled by default on Ubuntu kernels.
>
> http://lxr.linux.no/linux+v3.1.3/drivers/md/Kconfig#L157
>
> config MULTICORE_RAID456
>        bool "RAID-4/RAID-5/RAID-6 Multicore processing (EXPERIMENTAL)"
>        depends on MD_RAID456
>        depends on SMP
>        depends on EXPERIMENTAL
>        ---help---
>          Enable the raid456 module to dispatch per-stripe raid operations
> to a
>          thread pool.
>
>          If unsure, say N.
>
> $ grep MULTICORE_RAID456 /boot/config-3.0.0-1*
> /boot/config-3.0.0-12-generic:# CONFIG_MULTICORE_RAID456 is not set
> /boot/config-3.0.0-13-generic:# CONFIG_MULTICORE_RAID456 is not set
>
> It looks like a work in progress, I hope you have nothing to lose on those
> disks.
> See the linux-raid list for more information:
> http://marc.info/?l=linux-raid .
>
> Peter
>
> >
> > thanks mark
> >
> >
>
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