You know what, let me try just that today, I have a new install to do, so I'll try pre-creating a RAID10 on install and report back. First I'll try layered MD devices and then I'll try creating a RAID10 md device and we'll see if it can even boot off them.
Ok, I verified that inside anaconda one cannot create layered MD RAID arrays because once one forms an array there is no choice to create a volume of type "Software RAID". The RAID choices are RAID0, RAID1, RAID5 or RAID6 during install, no RAID10.
I can create multiple RAID1s though, of type "LVM Physical Volume" and then create a volume group composed of those. I can then create a root LV and a swap LV, though these will not be striped because LVM doesn't default to striping PVs, but concatenating, so in order to stripe these I'll need to leave enough free space to create striped versions, dump and restore from the old root to the new root and then edit the fstab/grub, run mkinitrd and reboot. Not exactly convenient, but unfortunate due to LVM's default policy of concatenating PVs instead of striping them... oh well.
As far as creating a RAID10 at the command prompt, the dm-raid10 kernel module is missing from the install image, so no luck directly creating a RAID10, and after a couple of reboots I was able to create a layered setup, but anaconda didn't recognize it (either immediately, or after a reboot) to be able to perform an install on it because it doesn't start the arrays upon startup to be able to find the nested one.
No surprise about raid10. I take it you tried this with Centos 5? Thanks for the testing. I cannot believe that it is no longer possible in Centos4/RHEL4 and later. I had done it too with Fedora Core 2 which is 2.6.4 based.
So if it worked for you in RH9, it no longer works anymore.
Maybe because RH9 had a separate MD RAID implementation and not the device-mapper implementation.
RH9 was 2.4 and had no fancy dm. BTW, md raid is still separate. But you have already said in your other post.