md.c patch for root on RAID-10

md.c patch for root on RAID-10

[Andrew Pam]

I have a server that is configured with the root partition on a RAID-10
array (/dev/md5 is RAID-1 /dev/md[34], /dev/md3 is RAID-0 /dev/sd[ab]2,
/dev/md4 is RAID-0 /dev/sd[cd]2).

This server boots Linux kernel 2.6.3 off /dev/md0 RAID-1 /dev/sd[abcd]1
(about to upgrade to 2.6.5) but unfortunately requires a complicated
custom initrd to boot correctly since the RAID autorun code does not
appear to autostart multilayer RAID arrays.  Can you offer me any
assistance in patching md.c to make it check if any autostarted RAID
arrays are themselves components of other RAID arrays that should also
be autostarted?

Thanks,
	Andrew Pam
-- 
mailto:xanni@xanadu.net                         Andrew Pam
http://www.xanadu.com.au/                       Chief Scientist, Xanadu
http://www.glasswings.com.au/                   Technology Manager, Glass Wings
http://www.sericyb.com.au/                      Manager, Serious Cybernetics

Re: md.c patch for root on RAID-10

[Neil Brown]

On Wednesday April 21, xanni@glasswings.com.au wrote:
> I have a server that is configured with the root partition on a RAID-10
> array (/dev/md5 is RAID-1 /dev/md[34], /dev/md3 is RAID-0 /dev/sd[ab]2,
> /dev/md4 is RAID-0 /dev/sd[cd]2).
> 
> This server boots Linux kernel 2.6.3 off /dev/md0 RAID-1 /dev/sd[abcd]1
> (about to upgrade to 2.6.5) but unfortunately requires a complicated
> custom initrd to boot correctly since the RAID autorun code does not
> appear to autostart multilayer RAID arrays.  Can you offer me any
> assistance in patching md.c to make it check if any autostarted RAID
> arrays are themselves components of other RAID arrays that should also
> be autostarted?

The simplest approach is to add a kernel parameter which will assemble
md5:

   md=5,/dev/md3,/dev/md4 root=/dev/md5

If that doesn't work, let me know and I will fix it.

ByTheWay, you have your raid10 upside-down.
It is more reliable to build raid1 arrays out of real drives, and then
a raid0 out of the raid1s.

NeilBrown