[dm-devel] RAID5 support ?

[Neil Brown]

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?

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.

NeilBrown