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I'm running Gentoo Linux with a custom compiled kernel and I've just migrated from a 2.6 kernel to a 3.5.

As my HD's are on RAID 0 mode I use a custom initrd file in order to be able to boot. While kernel 2.6 is able to boot without problems the new 3.5 compiled kernel fails to boot complaining about no block devices found. After taking a look at initrd.cpio contained scripts I can see the failure message is given by mdadm tool.

Does anyone has a clue about that?

Edit: this morning i noticed there was some kind of issue on my old initrd which works fine for 2.6 kernels, so created a new initrd which works fine and let me to boot into GNU/Gentoo Linux with same 3.5 bzImage.

It could be an issue of mdadm, gonna check it.
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Did you also update the rest of your system? BTW, you would probably have better luck getting an answer on the gentoo-users mailing list. – Keith Oct 26 '12 at 16:14

A new kernel usually requires a new initrd.

With the generated (genkernel) initrd, there is the scandelay=<seconds> boot parameter which has proven helpful to me in the past. On one of my boxes, mdadm ran before all devices were available and failed to assemble the /dev/mdX device where the root partition resides.

If I understand correctly (from looking at /usr/share/genkernel/defaults/initrd.scripts), scandelay forces the script to hang around while udev to settles, before assembling any software arrays and before trying to mount the real root partition.

Try a scandelay of 3-10 seconds.

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