There were some hurdles i had to overcome, and would like to report them :
* GRUB2 issues * Genkernel issues
GRUB2 issues :
Currently with grub2 on funtoo , if i am using dmraid and gpt partition scheme, grub2 fails to work. Talking on #grub2 on freenode, advice was given to try the following : ( quoting )
[01:58] <Jordan_U> pereira_alex: I may a a vegue idea of what's wrong. Either boot the desktop and run "ls" from the rescue shell and tell me the output, or run "grub-install --modules=part_gpt /dev/mapper/foo -- boot-directory=/path/to/boot/directory/" and try booting again, or (best) do both.
[02:05] <Jordan_U> phcoder: Do you think it's possible that somehow grub-probe is thinking that the partition containing /boot/ is actually a drive, and therefore setting up a cross disk install with no partmap module much like what happens with (non kpartx) loopback installs?
After following the advice to include --modules=part_gpt on the grub- install command line, it installed grub properly.
Note : ( which i still have to test ) It might be possible that this bug is known, and should be fixed on grub 1.99.
Genkernel issues :
After booting from grub, the initramfs cannot find the device for my Fake Raid GPT partition. This is because of one issue that DMRAID does not auto detect GPT partitions. I do have the devices on /dev/mapper/ but only the disk, not the partition.
here it adds support for kpartx discovery of the partitions right after creating the disks with DMRAID.
so ... i hacked the initrd script on genkernel and added that support.
But another problem with genkernel is that upon adding multipath support ( to have kpartx ), it doesnt work. It fails to copy the necessary libs for kpartx to work, leaving me with at boot prompt with "missing libudev.so.0" for kpartx.
I managed to solve this i creating an overlay to initramfs with the necessary libs into it.
So after all this, it works :) it boots.
Grub2 issues : 1.98 seems to have a problem with GPT Fake RAID partitions. Could be solved with Grub2 1.99. Could it be updated ?
Genkernel issues : Genkernel seems to fail at creating multipath support ( making a usable kpartx). Also needs to add to script initrd on initramfs to do a kpartx -a /dev/ mapper/$device after each GPT device discovered.