Disregard my original comments regarding the dm-raid45 thing. That was just a wrong hunch, as the same module info is in both initrd images and so it is unlikely to be the cause.
I am less inclined to think this is a bug in mdadm, though I agree that this will probably get re-assigned to some other package. I need to check that this isn't a udev issue.
Based on a brief review of the bug you listed below, I don't think this is the same mdadm issue. This doesn't feel like am mdadm issue.
The raid5 module loads fine if I do it manually. It's just not being called or is being called incorrectly.
I will debug more tomorrow and update. Thanks Michael Prokop wrote:
>The problem is that the raid456 module is not being loaded by >initramfs. I manually loaded the module with "modprobe raid5", >assembled by arrays with mdadm, and was able to boot normally. >The initramfs file /conf/modules says "dm-raid45", but I suspect >it should say "dm-raid456".[...] This is http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=411172 - unrelated to mdadm and initramfs-tools but being a dmraid issue. I'm tending to reassign this bugreport to mdadm actually.