[dm-devel] RAID5 support ?

[Alan Hourihane]

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 ?

> 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.

Alan.