[dm-devel] RAID5 support ?
Heinz Mauelshagen
mauelshagen at redhat.com
Thu Nov 3 18:41:06 UTC 2005
On Thu, Nov 03, 2005 at 11:39:43AM +0000, Alan Hourihane wrote:
> On Thu, 2005-11-03 at 22:20 +1100, Neil Brown wrote:
> > On Thursday November 3, alanh at fairlite.demon.co.uk wrote:
> > >
> > > I mean "Load the kernel image from an md device" which is what it means
> > > to me too.
> > >
> > > So, you go on to say that booting from raid5 almost certainly requires
> > > bios support - so I'm back to needing the onboard Sil 3114 BIOS to
> > > handle that and then get md/dmraid to sort the rest out - which gets
> > > back to my original question on when device mapper would get RAID5
> > > support so that dmraid can handle the SIL RAID5 metadata.
> >
> > "device mapper" and "dmraid" are of course different things.
> > One is a kernel subsystem, the other is a configuration tool.
> > For dmraid to be able to handle SIL RAID5, it is not necessary for
> > "device mapper" to get RAID5 support, only for dmraid to have
> > appropriate access to some sort of raid5 support in the Linux kernel.
> >
> > I would like md/raid5 (which is quite separate from device mapper) to
> > be able to provide the required level of support so that if the dmraid
> > developers so chose, they could use it rather than needing a second
> > raid5 implementation in the kernel. Hence my original question, asking
> > "how md/raid5 can be made to be sufficient" for the needs for dmraid?
>
> So what exactly is Heinz working on if it isn't support for RAID5 in
> device-mapper ?
It is a RAID4 and RAID5 device-mapper target.
>
> > I suspect all it needs is to be able to interface with a user-space
> > metadata handler, and possibly some extra configuration options to
> > match the expected functionality of the SiL.
> > The former I hope be possible by 2.6.16. The later I'm interested in
> > advice on.
>
> I'll defer to Heinz to make that choice - he's a lot closer to the code.
The device-mapper kernel subsystem aims to avoid multiple drivers for
block device virtualization being implemented seperately in the Linux
kernel by adding device-mapper targets as we go.
Implementing a target for RAID4 and RAID5 is just the long term approach
to get more mappings supported by device-mapper in order to minimize code
duplication.
>
> Alan.
>
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--
Regards,
Heinz -- The LVM Guy --
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Heinz Mauelshagen Red Hat GmbH
Consulting Development Engineer Am Sonnenhang 11
Cluster and Storage Development 56242 Marienrachdorf
Germany
Mauelshagen at RedHat.com +49 2626 141200
FAX 924446
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