intel fakeraid (imsm) linux kernel support

Hi all,

I am trying to find out if it is possible to:

a) Have the linux kernel autodetect / auto-assemble the fakeraid (to
avoid having an initrd (for speed and KISS))

b) Boot linux kernel from a fakeraid this: grub2? lilo? ... anything?

About (a):
Is it possible to autodetect any intel fakeraid (imsm)?
If yes: What RAID-Levels are supported? Especially what would I need to do to get my RAID-0 auto-assembled? If no: Are there plans?

About (b):
What boot-loader support to assemble the intel fakeraid to read the kernel from it - e.g. are able to assemble the /boot partition on the RAID (especially: level 0)? According to this wiki entry:
http://wiki.neuralbs.com/index.php/Gentoo_Quick_Install_notes#GRUB2
grub2 should support imsm (but grep for imsm in the Bazaar checkout does not yield any hit) <<< I also contacted the grub2 mailing-list for clarification I learned today that Ubuntu seems to be able to boot from a RAID-0 with grub2 (v1.98-1ubuntu7) and seemingly installed to /dev/mapper/isw_*. So far I only tried to install vanilla grub 1.98 to the mdadm v3 devices /dev/md12[67], without success.
In the documentation of grub2 (afaik) they don't distinguish between mdadm/dmraid software raid, they just state that grub2 works with software raid.

Side-Question:
To be able to have the kernel auto-assemble / autodetect any [e.g. mdadm] linux software RAID-0 you need *partions*, right? --> You can't assemble a software raid-0 using two complete drives:
/dev/sda
/dev/sdb
But you need to create e.g.:
/dev/sda1 <<< type set to FD
/dev/sdb1 <<< type set to FD

It would be great and very kind if someone could clarify these things for me (just a link to read the answers somewhere would work too ;). Thanks a lot!

Knuth

P.S.:
I adore Intels engagement for linux. Unfortunately is there no website (yet?) "intellinuxraid.org" (like there is: intellinuxgraphics.org).

The only official information from intel (google: intel raid linux) I could dig up so fare states: imsm is supported with mdadm >=v3 and dmraid >=v1. That leaves a lot of questions (eg. I never saw any details on how the intel software raid format works - e.g. I noticed that the first physical device of my RAID-0 seems to have the primary paritions, all the other RAID-0 devices are unpartitioned).

Hi, I think I answered these in my other response:

http://marc.info/?l=linux-raid&m=128206374710903&w=2

...but you specifically ask about partition-type-0xfd below:

[..]

You need partitions and the v0.90 metadata format.

You can, but not if you want to autodetect it. But just use an initrd and be happy :-)

One of the biggest differences between the native-md (0.90 and 1.x) formats and external (imsm and ddf) formats, is that the latter only use complete drives. For example if you wanted two raid0 arrays on the same set of disks using a native-md format you would need to partition the disks first and then:

mdadm -C /dev/md0 /dev/sd[a-d]1 -n 4 - l 0
mdadm -C /dev/md1 /dev/sd[a-d]2 -n 4 -l 0

...with the external formats you create a container of disks and then carve multiple volumes out of that set:
mdadm -C /dev/md/imsm /dev/sd[a-d] -n 4 -e imsm # create an imsm container mdadm -C /dev/md0 /dev/md/imsm -n 4 -l 0 -z $size # create a raid0 array in the container
mdadm -C /dev/md1 /dev/md/imsm -n 4 -l 0 # use the remaining space for a second raid0 volume

The bios (on an enabled platform) will see /dev/md0 and /dev/md1 as bootable devices, not the individual component disks (/dev/sd[a-d]).

--
Dan
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